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  2. Collatz conjecture - Wikipedia

    en.wikipedia.org/wiki/Collatz_conjecture

    For instance, the first counterexample must be odd because f(2n) = n, smaller than 2n; and it must be 3 mod 4 because f 2 (4n + 1) = 3n + 1, smaller than 4n + 1. For each starting value a which is not a counterexample to the Collatz conjecture, there is a k for which such an inequality holds, so checking the Collatz conjecture for one starting ...

  3. Pascal's triangle - Wikipedia

    en.wikipedia.org/wiki/Pascal's_triangle

    For example, the initial number of row 1 (or any other row) is 1 (the sum of 0 and 1), whereas the numbers 1 and 3 in row 3 are added to produce the number 4 in row 4. Formula [ edit ] In Pascal's triangle, each number is the sum of the two numbers directly above it.

  4. List of prime numbers - Wikipedia

    en.wikipedia.org/wiki/List_of_prime_numbers

    Of the form 2 2 n + 1. 3, 5, 17, 257, 65537 (OEIS: A019434) As of June 2024 these are the only known Fermat primes, and conjecturally the only Fermat primes. The probability of the existence of another Fermat prime is less than one in a billion. Generalized Fermat primes. Of the form a 2 n + 1 for fixed integer a.

  5. Mental calculation - Wikipedia

    en.wikipedia.org/wiki/Mental_calculation

    The product of two variables ranging from 90-99 will result in a 4-digit number. The first step is to find the ones-digit and the tens digit. Subtract both variables from 100 which will result in 2 one-digit number. The product of the 2 one-digit numbers will be the last two digits of one's final product.

  6. Mathematics of Sudoku - Wikipedia

    en.wikipedia.org/wiki/Mathematics_of_Sudoku

    Mathematical context. The general problem of solving Sudoku puzzles on n2 × n2 grids of n × n blocks is known to be NP-complete. [8] A puzzle can be expressed as a graph coloring problem. [9] The aim is to construct a 9-coloring of a particular graph, given a partial 9-coloring. The Sudoku graph has 81 vertices, one vertex for each cell.

  7. Composite number - Wikipedia

    en.wikipedia.org/wiki/Composite_number

    A composite number is a positive integer that can be formed by multiplying two smaller positive integers. Equivalently, it is a positive integer that has at least one divisor other than 1 and itself. [1] [2] Every positive integer is composite, prime, or the unit 1, so the composite numbers are exactly the numbers that are not prime and not a ...

  8. Emirp - Wikipedia

    en.wikipedia.org/wiki/Emirp

    An emirp (prime spelled backwards) is a prime number that results in a different prime when its decimal digits are reversed. This definition excludes the related palindromic primes. The term reversible prime is used to mean the same as emirp, but may also, ambiguously, include the palindromic primes.

  9. RSA numbers - Wikipedia

    en.wikipedia.org/wiki/RSA_numbers

    RSA numbers. In mathematics, the RSA numbers are a set of large semiprimes (numbers with exactly two prime factors) that were part of the RSA Factoring Challenge. The challenge was to find the prime factors of each number. It was created by RSA Laboratories in March 1991 to encourage research into computational number theory and the practical ...