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

Author

Hugo Pfoertner, Aug 28 2022

Keywords

• nonn

Examples

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

Crossrefs

Cf. A000142, A046388, A131057.

Programs

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

Extensions

More terms from Jinyuan Wang, Aug 28 2022