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List the cuban primes

The number 61 is a cuban prime because it is prime and the difference two cubes, 64 and 125. Write a function to list the cuba...

8 meses ago

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Easy Sequences 35: Cutting a donut to Semi-prime pieces

The figure below illustrates how a torus (donut shape) can be cut in pieces with only cuts: ...

8 meses ago

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Easy Sequences 37: Natural Factorable Polynomials

A polynomial of the form: , for , is said to be natural factorable if it can be factored into products of first degree binomials...

8 meses ago

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Easy Sequences 36: Hyperbolic Lattice Points

The graph, shown below, of the hyperbola: , passes through four positive lattice points:. ...

8 meses ago

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Easy Sequences 34: Modified Pascal's Triangle

Consider the integer triangle below: It follows the same ...

8 meses ago

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Easy Sequences 22: Sum of Proper Fractions

Let 'F' be the set of all proper fractions in lowest term, whose denominator is less than or equal 'd'. So, for d = 10, we have:...

8 meses ago

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Easy Sequences 28: Sum of Radicals of Integers

The radical of a positive integer is defined as the product of the distinct prime numbers dividing . For example, the distinct ...

8 meses ago

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Easy Sequences 29: Odd proper divisors of odd proper divisors

The number is special. It has odd number of proper divisors: . Furthermore, if you take any of its proper divisors, say , it t...

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Easy Sequences 33: Web Trapped Ant

An ant is trapped on a spider web inside a can with open top. The can has a radius and height . A spider sitting on the outside...

8 meses ago

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List modest numbers up to n

After determining the nude numbers, or the numbers that openly display some of their divisors as their digits, one would think t...

8 meses ago

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Easy Sequences 21: Combinatorial Summations

Create the function S(n), defined by the following summation: The symbol is the combination f...

8 meses ago

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Easy Sequences 31: N-N's Sequence

We define the N-N's Sequence, as the series of all positive integers in ascending order and with repetition, wherein a appears ...

8 meses ago

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Easy Sequences 25: Product of Series

The function 'P(n)' is defined as the series product: where 'T(n)' is the triangular sum: ...

8 meses ago

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Easy Sequences 23: Hat Guessing Game!

Consider the following Game Show: Hats, with numbers written on each, were placed on the heads of the participants. Participant...

8 meses ago

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Multiply binary numbers

Write a function to multiply two binary numbers input as strings. For example, input values of ‘1011’ and ‘101’ should give ’110...

8 meses ago

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Count the primes in Collatz sequences

Several Cody problems (21, 69, 42937, 44448, 44784, 52422) involve Collatz sequences. These start with a seed . If is odd, the ...

9 meses ago

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List the Moran numbers

The quotient of a Moran number and its digit sum is prime. For example, 117 and 481 are Moran numbers because 117/(1+1+7) is 13 ...

9 meses ago

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Easy Sequences 6: Coefficient sums of derivatives

Consider the polynomial function and its first-order derivative . The sums of the coefficients of P and P', are and , respecti...

9 meses ago

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Determine whether a number is a fibodiv number

The number 14 is a fibodiv number because you can divide it into 1 and 4, use those numbers as the seeds for a Fibonacci sequenc...

9 meses ago

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Determine whether a number is unprimeable

The number 204 is unprimeable because no single digit can be changed to make it prime. In contrast, the number 207 is not unprim...

9 meses ago

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Count the ways to draw non-intersecting chords between points on a circle

There are 9 ways to draw non-intersecting chords between four points on the perimeter of a circle (including no chords at all). ...

9 meses ago

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Find the nth nude number

The number 672 is a nude number because it openly displays three of its divisors: 6, 7, and 2. In other words, a nude number is ...

9 meses ago

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Easy Sequences 9: Faithful Pairs

A "faithful number" is a non-prime number that is one less or one more than some prime number but not both. For example, for num...

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Easy Sequences 10: Sum of Cumsums of Fibonacci Sequence

The function F(n) is defined as the set of Fibonacci numbers from the first up to the n-th. S(n) is the result of applying to F,...

9 meses ago

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Easy Sequences 8: Triangles with integer sides and prime perimeters

The triangle below is special. It has integer sides and a prime perimeter. Given an integer "n" we want to know how many t...

9 meses ago

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Hoax Numbers

A Hoax Number (OEIS A019506) is defined as a composite number, whose sum of digits is equal to the sum of digits of its distinct...

9 meses ago

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Easy Sequences 3: Prime 44-number Squares

The positive integers 62 and 238 are related. Their squares (3844 and 56,644) both end in '44'. In fact, 62 and 238 are the 3rd ...

10 meses ago

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Easy Sequences 2: Trigonometric function with integral input and output

The function 'F', defined as: , will always return an integer if the input is a natural number (in radian...

10 meses ago

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Double Fibonacci

double_fibonacci takes two integers, each greater than one, as input arguments (it does not have to check the format of the inpu...

10 meses ago

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Sort Except Zeros

Sort the numbers in a vector. But the position of zeros should not be changed. Example: sort_except_zeros( [5 3 0 0 2 4] ) == [...

10 meses ago