A085274 Composite k such that (k!/k#) + 1 is a semiprime, where k# = primorial numbers A034386.

6, 10, 21, 22, 24, 25, 27, 30, 39, 48, 52, 57, 65, 87, 94, 110, 114, 124, 156, 161

Offset: 1

Author

Jason Earls, Aug 12 2003

Keywords

• nonn

Comments

n!/n# is called n compositorial. The actual sequence is (6,7),(10,11),21,(22,23),24,25,27,(30,31),39,48, (52,53),57,65,... where the values in parenthesis yield the same semiprime.

That is, since p!/p# = (p-1)!/(p-1)#, primes never appear in this sequence. - Sean A. Irvine, Jun 30 2020

Examples

			25!/25# + 1 is a product of two primes: 69528040243200001 = 2594807 * 26795071943.
		

Links

• Hisanori Mishima, Compositorial + 1 (n = 4 to 150).

Crossrefs

Cf. A001358, A049420, A049614.

Extensions

More terms from Robert G. Wilson v, Aug 15 2003

Offset corrected and a(19) and a(20) from Sean A. Irvine, Jun 30 2020