A356207 a(n) is the difference between n! and the next smaller odd squarefree semiprime (A046388).

3, 1, 3, 7, 1, 7, 1, 5, 3, 1, 19, 11, 1, 19, 19, 11, 1, 19, 23, 1, 1, 47, 1, 1, 29, 3, 29, 31, 59, 73, 1, 43, 1, 13, 17, 41, 1, 5, 5, 3, 53, 79, 7, 1, 53, 23, 1, 13, 13, 61, 7, 59, 61, 7, 31, 1, 89, 107, 103, 67, 47, 103, 19, 43, 1, 71, 11, 7, 83, 79, 67, 71, 29

Offset

4,1

Links

Table of n, a(n) for n=4..76.

Example

a(4) = 3 = 4! - 3*7;
a(5) = 1 = 5! - 7*17;
a(6) = 3 = 6! - 3*239.

Prog

(PARI) isok(k) = my(f=factor(k)); (bigomega(f) == 2) && (omega(f)==2)
a(n) = my(k=n!-1); while (!isok(k), k-=2); n!-k; \\ Michel Marcus, Aug 29 2022

Crossrefs

Cf. A000142, A046388, A131057.

Sequence in context: A209566 A208916 A209766 * A114972 A107461 A035619

Adjacent sequences: A356204 A356205 A356206 * A356208 A356209 A356210

Keyword

nonn

Author

Hugo Pfoertner, Aug 28 2022

Extensions

More terms from Jinyuan Wang, Aug 28 2022

Status

approved