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

1,1

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

Links

Table of n, a(n) for n=1..20.

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

Example

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

Crossrefs

Cf. A001358, A049420, A049614.

Sequence in context: A065758 A348838 A254028 * A175648 A178661 A190273

Adjacent sequences: A085271 A085272 A085273 * A085275 A085276 A085277

Keyword

nonn

Author

Jason Earls, Aug 12 2003

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

Status

approved