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 A085274 Composite k such that (k!/k#) + 1 is a semiprime, where k# = primorial numbers A034386. 0
 6, 10, 21, 22, 24, 25, 27, 30, 39, 48, 52, 57, 65, 87, 94, 110, 114, 124, 156, 161 (list; graph; refs; listen; history; text; internal format)
 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

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Last modified April 20 22:14 EDT 2024. Contains 371848 sequences. (Running on oeis4.)