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  2. Table of divisors - Wikipedia

    en.wikipedia.org/wiki/Table_of_divisors

    Plot of the number of divisors of integers from 1 to 1000. Highly composite numbers are in bold and superior highly composite numbers are starred. ... 10, 12, 15, 20 ...

  3. Divisibility rule - Wikipedia

    en.wikipedia.org/wiki/Divisibility_rule

    The basic rule for divisibility by 4 is that if the number formed by the last two digits in a number is divisible by 4, the original number is divisible by 4; [2] [3] this is because 100 is divisible by 4 and so adding hundreds, thousands, etc. is simply adding another number that is divisible by 4. If any number ends in a two digit number that ...

  4. List of integer sequences - Wikipedia

    en.wikipedia.org/wiki/List_of_integer_sequences

    0, 1, 3, 6, 2, 7, 13, 20, 12, 21, 11, 22, 10, 23, 9, 24, 8, 25, 43, 62, ... "subtract if possible, otherwise add" : a (0) = 0; for n > 0, a ( n ) = a ( n − 1) − n if that number is positive and not already in the sequence, otherwise a ( n ) = a ( n − 1) + n , whether or not that number is already in the sequence.

  5. 12 (number) - Wikipedia

    en.wikipedia.org/wiki/12_(number)

    12 (twelve) is the natural number following 11 and preceding 13.. Twelve is the 3rd superior highly composite number, [1] the 3rd colossally abundant number, [2] the 5th highly composite number, and is divisible by the numbers from 1 to 4, and 6, a large number of divisors comparatively.

  6. Weird number - Wikipedia

    en.wikipedia.org/wiki/Weird_number

    In number theory, a weird number is a natural number that is abundant but not semiperfect. [ 1 ] [ 2 ] In other words, the sum of the proper divisors ( divisors including 1 but not itself) of the number is greater than the number, but no subset of those divisors sums to the number itself.

  7. Factorial - Wikipedia

    en.wikipedia.org/wiki/Factorial

    In mathematics, the factorial of a ... is divisible by all prime numbers that are at most ... The values 12! and 20! are the largest factorials that can be stored in, ...

  8. Euler's totient function - Wikipedia

    en.wikipedia.org/wiki/Euler's_totient_function

    In words: the distinct prime factors of 20 are 2 and 5; half of the twenty integers from 1 to 20 are divisible by 2, leaving ten; a fifth of those are divisible by 5, leaving eight numbers coprime to 20; these are: 1, 3, 7, 9, 11, 13, 17, 19.

  9. Twin prime - Wikipedia

    en.wikipedia.org/wiki/Twin_prime

    A twin prime is a prime number that is either 2 less or 2 more than another prime number—for example, either member of the twin prime pair (17, 19) or (41, 43). In other words, a twin prime is a prime that has a prime gap of two. Sometimes the term twin prime is used for a pair of twin primes; an alternative name for this is prime twin or ...