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  2. 169 (number) - Wikipedia

    en.wikipedia.org/wiki/169_(number)

    169 is an odd number, a composite number, and a deficient number. 169 is a square number: 13 × 13 = 169, and if each number is reversed the equation is still true: 31 × 31 = 961. 144 shares this property: 12 × 12 = 144, 21 × 21 = 441. 169 is one of the few squares to also be a centered hexagonal number. [1]

  3. Parity (mathematics) - Wikipedia

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

    Even and odd numbers have opposite parities, e.g., 22 (even number) and 13 (odd number) have opposite parities. In particular, the parity of zero is even. [2] Any two consecutive integers have opposite parity. A number (i.e., integer) expressed in the decimal numeral system is even or odd according to whether its last digit is even or odd. That ...

  4. Table of prime factors - Wikipedia

    en.wikipedia.org/wiki/Table_of_prime_factors

    The Liouville function λ(n) is 1 if Ω(n) is even, and is -1 if Ω(n) is odd. The Möbius function μ(n) is 0 if n is not square-free. Otherwise μ(n) is 1 if Ω(n) is even, and is −1 if Ω(n) is odd. A sphenic number has Ω(n) = 3 and is square-free (so it is the product of 3 distinct primes).

  5. Square number - Wikipedia

    en.wikipedia.org/wiki/Square_number

    Squares of odd numbers are odd, and are congruent to 1 modulo 8, since (2n + 1) 2 = 4n(n + 1) + 1, and n(n + 1) is always even. In other words, all odd square numbers have a remainder of 1 when divided by 8. Every odd perfect square is a centered octagonal number. The difference between any two odd perfect squares is a multiple of 8.

  6. Erdős–Straus conjecture - Wikipedia

    en.wikipedia.org/wiki/Erdős–Straus_conjecture

    Even without this relaxation, the Erdős–Straus conjecture is difficult only for odd ... except possibly those that are 1, 121, 169, 289, 361, or 529 mod 840. The ...

  7. Parity of a permutation - Wikipedia

    en.wikipedia.org/wiki/Parity_of_a_permutation

    The permutation is odd if and only if this factorization contains an odd number of even-length cycles. Another method for determining whether a given permutation is even or odd is to construct the corresponding permutation matrix and compute its determinant. The value of the determinant is the same as the parity of the permutation. Every ...

  8. Even and odd functions - Wikipedia

    en.wikipedia.org/wiki/Even_and_odd_functions

    They are named for the parity of the powers of the power functions which satisfy each condition: the function () = is even if n is an even integer, and it is odd if n is an odd integer. Even functions are those real functions whose graph is self-symmetric with respect to the y -axis, and odd functions are those whose graph is self-symmetric ...

  9. 165 (number) - Wikipedia

    en.wikipedia.org/wiki/165_(number)

    an odd number, a composite number, and a deficient number. a sphenic number. a tetrahedral number. [1] the number of prime knots with 10 crossings. [2] the sum of the sums of the divisors of the first 14 positive integers. [3] a self number in base 10. a palindromic number in binary (10100101 2) and bases 14 (BB 14), 32 (55 32) and 54 (33 54).