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Happy 2013...
Happy 2013, everyone! An interesting tidbit about 2013 is that it is the first year since 1987 to contain four different digits...

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Largest Twin Primes
<http://en.wikipedia.org/wiki/Twin_prime Twin primes> are primes p1, p2 = p1 + 2 such that both p1 and p2 are prime numbers. Giv...

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Lychrel Number Test (Inspired by Project Euler Problem 55)
The task for this problem is to create a function that takes a number _n_ and tests if it might be a Lychrel number. This is, re...

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Determine if input is a perfect number
A <http://en.wikipedia.org/wiki/Perfect_number/ perfect number> occurs whent the sum of all divisors of a positive integer, exce...

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Determine if input is a Narcissistic number
<http://en.wikipedia.org/wiki/Narcissistic_number Narcissistic number> is a number that is the sum of its own digits each raised...

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Mersenne Primes
A Mersenne prime is a prime number of the form M = 2^p - 1, where p is another prime number. For example, 31 is a Mersenne prim...

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Numbers with prime factors 2, 3 and 5.
Make a function which takes one positive integer n and returns a matrix with the numbers of the form (2^i)*(3^j)*(5^k) which are...

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Recurring Cycle Length (Inspired by Project Euler Problem 26)
Preface: This problem is inspired by <http://projecteuler.net/problem=26 Project Euler Problem 26> and uses text from that quest...

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Project Euler: Problem 9, Pythagorean numbers
A Pythagorean triplet is a set of three natural numbers, a b c, for which, a^2 + b^2 = c^2 For example, 3^2 + 4^2 = 9 + 16 ...

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First N Perfect Squares
*Description* Return the first N perfect squares *Example* input = 4; output = [ 1 4 9 16 ];

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Reverse within string
If input is a string 'yellow' the output should be 'leywol'. Locate the middle of the string and reverse the first (yel) and sec...

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Solve the Challenger puzzle

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Index one element in each vector of an array along a given dimension
Functions like min and max can return in their second output argument the index of the element in each vector along a particular...

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Sort numbers by outside digits
Sort the array so that they are sorted as if their value was a 5 digit number made from the first three and last two digits of t...

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Index of a Rational number
The set of real numbers are infinite. They are so many that real numbers can't even be enumerated. However, unlike real numbers ...

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Tridiagonal
Return an n-by-n matrix that has a, b, c as the subdiagonal, main diagonal, and superdiagonal entries in the matrix. Example ...

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Find the maximum two numbers of every column of a matrix
Find the maximum two numbers of every column of a matrix. Example: If we input a matrix A = [ 1 2 4 6 0 3 ...

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Finding neighbors of [-1:1] in a matrix....
Hello All! Well I found this one fun to figure out, all you have to do is make a matrix of 1's or 0's (true or false) that sh...

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How unique?
Sometimes, when we check unique entries of vector we would like to know how many times each value occurs. Given vector of num...

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Another colon problem
This is simple problem based on problems 555, 801, 1118, etc. Create an index vector from two input vectors. Example: ...

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return row and column indices given 2 values which define a range
Inspired by problem <http://www.mathworks.co.kr/matlabcentral/cody/problems/856-getting-the-indices-from-a-matrice> Inputs: - ...

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Sum of odd numbers in a matrix
Find the sum of all the odd numbers in a matrix. Example x = [2 3 5 7 1 4 11] y = 27

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Find the index of n in magic(n)
If input n=5, then magic(n) is 17 24 1 8 15 23 5 7 14 16 4 6 13 20 22...

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Replace pattern 0 1 0 and 1 0 1
Find and replace a pattern in a row of zeroes and ones. * Find 1 0 1 and replace it with 1 1 1 * Find 0 1 0 and replace it w...

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Largest territory
Determine whose territory is largest. If there are multiple numbers tied for the largest territory, return the smallest number. ...

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counting groups!
This problem is about counting groups. Example If you have x: x = [0.8 0.8 0.8 0.3 0.3 0.4 0.5 0.6 0.6 0.9] then a...

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Three...is a magic number.
Yes it is... It's a magic number... To help you get rid of that earworm, here's a new Cody problem. You are given a squar...

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Time Expansion
How can you slow down any discrete-time signal? Example Input original signal x. x = [1 2 3 -1 -2 -5 -4] We want t...

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Back to basics - mean of corner elements of a matrix
Calculate the mean of corner elements of a matrix. e.g. a=[1 2 3; 4 5 6; 7 8 9;] Mean = (1+3+7+9)/4 = 5

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remove single elements
Given a vector of integers, remove the elements that have appeared only once. The output elements should be in exact order as th...

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