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  2. 142857 - Wikipedia

    en.wikipedia.org/wiki/142857

    142857 2 = 142857 × 142857 = 20408122449 20408 + 122449 = 142857. Multiplying by a multiple of 7 will result in 999999 through this process: 142857 × 7 4 = 342999657 342 + 999657 = 999999. If you square the last three digits and subtract the square of the first three digits, you also get back a cyclic permutation of the number. [citation ...

  3. Factorial number system - Wikipedia

    en.wikipedia.org/wiki/Factorial_number_system

    The factorial number system is a mixed radix numeral system: the i-th digit from the right has base i, which means that the digit must be strictly less than i, and that (taking into account the bases of the less significant digits) its value is to be multiplied by (i − 1)!

  4. Transposable integer - Wikipedia

    en.wikipedia.org/wiki/Transposable_integer

    An integral multiplier refers to the multiplier n being an integer: . An integer X shift right cyclically by k positions when it is multiplied by an integer n.X is then the repeating digits of 1 ⁄ F, whereby F is F 0 = n 10 k − 1 (F 0 is coprime to 10), or a factor of F 0; excluding any values of F which are not more than n.

  5. Napier's bones - Wikipedia

    en.wikipedia.org/wiki/Napier's_bones

    Napier's bones for 4, 2, and 5 are placed into the board, in sequence. These bones show the larger figure which will be multiplied. These bones show the larger figure which will be multiplied. The numbers lower in each column, or bone, are the digits found by ordinary multiplication tables for the corresponding integer, positioned above and ...

  6. List of numeral systems - Wikipedia

    en.wikipedia.org/wiki/List_of_numeral_systems

    "A base is a natural number B whose powers (B multiplied by itself some number of times) are specially designated within a numerical system." [1]: 38 The term is not equivalent to radix, as it applies to all numerical notation systems (not just positional ones with a radix) and most systems of spoken numbers. [1]

  7. Persistence of a number - Wikipedia

    en.wikipedia.org/wiki/Persistence_of_a_number

    The additive persistence of 2718 is 2: first we find that 2 + 7 + 1 + 8 = 18, and then that 1 + 8 = 9. The multiplicative persistence of 39 is 3, because it takes three steps to reduce 39 to a single digit: 39 → 27 → 14 → 4. Also, 39 is the smallest number of multiplicative persistence 3.

  8. Mental calculation - Wikipedia

    en.wikipedia.org/wiki/Mental_calculation

    1 3 = 1 up 1; 2 3 = 8 down 3; 3 3 = 27 down 1; 4 3 = 64 down 3; 5 3 = 125 up 1; 6 3 = 216 up 1; 7 3 = 343 down 3; 8 3 = 512 down 1; 9 3 = 729 down 3; 10 3 = 1000 up 1; There are two steps to extracting the cube root from the cube of a two-digit number. For example, extracting the cube root of 29791. Determine the one's place (units) of the two ...

  9. Multiply perfect number - Wikipedia

    en.wikipedia.org/wiki/Multiply_perfect_number

    It can be proven that: . For a given prime number p, if n is p-perfect and p does not divide n, then pn is (p + 1)-perfect.This implies that an integer n is a 3-perfect number divisible by 2 but not by 4, if and only if n/2 is an odd perfect number, of which none are known.