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  2. Factorion - Wikipedia

    en.wikipedia.org/wiki/Factorion

    For =, the sum of the factorials of the digits is simply the number of digits in the base 2 representation since ! =! =. A natural number n {\displaystyle n} is a sociable factorion if it is a periodic point for SFD b {\displaystyle \operatorname {SFD} _{b}} , where SFD b k ⁡ ( n ) = n {\displaystyle \operatorname {SFD} _{b}^{k}(n)=n} for a ...

  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. Factorial - Wikipedia

    en.wikipedia.org/wiki/Factorial

    Here () denotes the sum of the base-digits of , and the exponent given by this formula can also be interpreted in advanced mathematics as the p-adic valuation of the factorial. [54] Applying Legendre's formula to the product formula for binomial coefficients produces Kummer's theorem , a similar result on the exponent of each prime in the ...

  5. Legendre's formula - Wikipedia

    en.wikipedia.org/wiki/Legendre's_formula

    Since ! is the product of the integers 1 through n, we obtain at least one factor of p in ! for each multiple of p in {,, …,}, of which there are ⌊ ⌋.Each multiple of contributes an additional factor of p, each multiple of contributes yet another factor of p, etc. Adding up the number of these factors gives the infinite sum for (!

  6. Derangement - Wikipedia

    en.wikipedia.org/wiki/Derangement

    In this case the problem reduces to n − 2 people and n − 2 hats, because P 1 received h i ' s hat and P i received h 1 's hat, effectively putting both out of further consideration. For each of the n − 1 hats that P 1 may receive, the number of ways that P 2, ..., P n may all receive hats is the sum of the counts for the two cases.

  7. Digit sum - Wikipedia

    en.wikipedia.org/wiki/Digit_sum

    The concept of a decimal digit sum is closely related to, but not the same as, the digital root, which is the result of repeatedly applying the digit sum operation until the remaining value is only a single digit. The decimal digital root of any non-zero integer will be a number in the range 1 to 9, whereas the digit sum can take any value.

  8. HackerRank - Wikipedia

    en.wikipedia.org/wiki/HackerRank

    HackerRank's programming challenges can be solved in a variety of programming languages (including Java, C++, PHP, Python, SQL, and JavaScript) and span multiple computer science domains. [ 2 ] HackerRank categorizes most of their programming challenges into a number of core computer science domains, [ 3 ] including database management ...

  9. Factorial code - Wikipedia

    en.wikipedia.org/wiki/Factorial_code

    To create factorial codes, Horace Barlow and co-workers suggested to minimize the sum of the bit entropies of the code components of binary codes (1989). Jürgen Schmidhuber (1992) re-formulated the problem in terms of predictors and binary feature detectors, each receiving the raw data as an input. For each detector there is a predictor that ...