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List odd twin composites
Twin primes, or prime numbers that differ by 2 (e.g., 17 and 19, 59 and 61, or 191 and 193), are the subject of several Cody pro...

1 year ago

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List the Euclid numbers
Euclid proved that the number of primes is infinite with the following argument. Suppose the primes form a finite set , , . Comp...

1 year ago

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List the Beatriz numbers
Write a function to find integers less than or equal to an input value that solve the equation . The function gives the sum o...

1 year ago

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Compute the largest number whose prime factors sum to n
This problem deals with a sequence whose tenth term is 36 because the prime factors of 36 (2, 2, 3, 3) sum to 10. The number 32 ...

1 year 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 ...

1 year ago

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Solve the arithmetic differential equation D(n) = n

1 year ago

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Compute the arithmetic derivative of integers

1 year ago

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List composite numbers that cannot be written as the sum of two primes

1 year ago

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Find pairs of primes with the same digit sum and a specified separation

1 year ago

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Identify prime words

1 year ago

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Play Outside In with primes
In the word game Outside In,* you start with a word, take the first and last letters, try to think of a word in which the two le...

1 year ago

Solved

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 ...

1 year 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...

1 year ago

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List prime anagrams of a number

1 year ago

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Find the smallest prime with n inside
Consider the sequence that begins 101, 113, 127, 131, 149, 151, 163,... Not only is every term prime, the th term is the smalles...

1 year ago

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List the nth prime quartet prefix
Prime numbers larger than 5 can end only in 1, 3, 7, or 9, but of course not all numbers ending in these four digits are prime. ...

1 year ago

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List Honaker primes
The number 131 is the 32nd prime number. It is a Honaker prime because the sum of its digits (1+3+1) equals the sum of the digit...

1 year ago

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Label primes with the Erdos-Selfridge classification

1 year ago

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List Proth primes

1 year ago

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Compute home primes in a given base

1 year ago

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Determine whether a number is a prime self number
Integers can be classified as generated numbers or self numbers. A generated number is one that can be expressed as the sum of a...

1 year ago

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List the good primes
The th prime is classified as “good” if for . For example, 5 is a good prime because is greater than and , but 7 is not beca...

1 year ago

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List the dihedral primes
The number 1880111 is a dihedral prime (or dihedral calculator prime) because on a seven-segment display it is prime (a) forward...

1 year ago

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List the delete-a-digit primes

1 year ago

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Play PRIMEGAME
Have you ever used the Sieve of Eratosthenes and said, "I wonder whether there’s a less efficient way to find prime numbers."? N...

1 year ago

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Create a sequence of primes p such that p > n π(p)

1 year ago

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Test approximations of the prime counting function

1 year ago

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Find jumping medalists

1 year ago

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Construct a prime circle
A <https://mathworld.wolfram.com/PrimeCircle.html prime circle> is a circular arrangement of the numbers 1 to 2n such that pairs...

1 year ago

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Test the generalized Legendre conjecture

1 year ago