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  2. Divisibility rule - Wikipedia

    en.wikipedia.org/wiki/Divisibility_rule

    And that is actually the same as subtracting 7×10 n (clearly a multiple of 7) from 10×10 n. Similarly, when you turn a 3 into a 2 in the following decimal position, you are turning 30×10 n into 2×10 n, which is the same as subtracting 30×10 n −28×10 n, and this is again subtracting a multiple of 7. The same reason applies for all the ...

  3. Abundant number - Wikipedia

    en.wikipedia.org/wiki/Abundant_number

    The smallest odd integer with abundancy index exceeding 3 is 1018976683725 = 3 3 × 5 2 × 7 2 × 11 × 13 × 17 × 19 × 23 × 29. [8] If p = (p 1, ..., p n) is a list of primes, then p is termed abundant if some integer composed only of primes in p is abundant. A necessary and sufficient condition for this is that the product of p i /(p i − ...

  4. List of types of numbers - Wikipedia

    en.wikipedia.org/wiki/List_of_types_of_numbers

    Prime number: A positive integer with exactly two positive divisors: itself and 1. The primes form an infinite sequence 2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, ... Composite number: A positive integer that can be factored into a product of smaller positive integers. Every integer greater than one is either prime or composite.

  5. 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.

  6. Least common multiple - Wikipedia

    en.wikipedia.org/wiki/Least_common_multiple

    For example, 10 is a multiple of 5 because 5 × 2 = 10, so 10 is divisible by 5 and 2. Because 10 is the smallest positive integer that is divisible by both 5 and 2, it is the least common multiple of 5 and 2. By the same principle, 10 is the least common multiple of −5 and −2 as well.

  7. Multiple (mathematics) - Wikipedia

    en.wikipedia.org/wiki/Multiple_(mathematics)

    In mathematics, a multiple is the product of any quantity and an integer. [1] In other words, for the quantities a and b, it can be said that b is a multiple of a if b = na for some integer n, which is called the multiplier.

  8. Palindromic number - Wikipedia

    en.wikipedia.org/wiki/Palindromic_number

    The first nine terms of the sequence 1 2, 11 2, 111 2, 1111 2, ... form the palindromes 1, 121, 12321, 1234321, ... (sequence A002477 in the OEIS ) The only known non-palindromic number whose cube is a palindrome is 2201, and it is a conjecture the fourth root of all the palindrome fourth powers are a palindrome with 100000...000001 (10 n + 1).

  9. Singly and doubly even - Wikipedia

    en.wikipedia.org/wiki/Singly_and_doubly_even

    This 4-fold and 8-fold periodicity in the structure of manifolds is related to the 4-fold periodicity of L-theory and the 8-fold periodicity of real topological K-theory, which is known as Bott periodicity. If a compact oriented smooth spin manifold has dimension n ≡ 4 mod 8, or ν 2 (n) = 2 exactly, then its signature is an integer multiple ...