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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
EXAMPLE
25!/25# + 1 is a product of two primes: 69528040243200001 = 2594807 * 26795071943.
CROSSREFS
Sequence in context: A065758 A348838 A254028 * A175648 A178661 A190273
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.)