This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
a(1) = 4 because 4 = 1! + 1! + 2!; a(2) = 8 because 8 = 1! + 1! + 3!; a(3) = 9 because 9 = 1! + 2! + 3!.
5041 = 71^2 = 1! + 7!.
/* To compile: gcc -Wall -O2 A227644.c -o A227644 -lgmp */ #include#include #include int main() { int bsz=256, a=0; mpz_t *f, t; f = malloc(sizeof(mpz_t) * bsz); mpz_init(t); mpz_init(f[0]); mpz_set_ui(f[0], 1); while (1) { a += 1; if (a == bsz) { bsz *= 2; f = (mpz_t *) realloc(f, sizeof(mpz_t) * bsz); } mpz_init(f[a]); mpz_mul_ui(f[a], f[a-1], a); for (int i=1; i<=a; i++) { mpz_add(t, f[a], f[i]); if (mpz_perfect_power_p(t)) { gmp_printf("%Zd, ", t); fflush(stdout); } } } return 0; }
1815848 = 122^3 = 2! + 3! + 6! + 6! + 9! + 9! + 9! + 9! + 9!.
729 = 3^6 = 1! + 2! + 3! + 6!.
5832 = 18^3 = 4! + 4! + 4! + 6! + 7!.
443556 = 666^2 = 3! + 3! + 4! + 8! + 8! + 9!.
83521 = 17^4 = 1! + 6! + 6! + 6! + 6! + 8! + 8!.
10890000 = 3300^2 = 6! + 6! + 6! + 6! + 6! + 10! + 10! + 10!.
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