A085725 Numbers k such that 1 + (product of first k primes) is a semiprime.

6, 8, 9, 14, 18, 19, 21, 23, 26, 34, 36, 40, 48, 54, 76, 88, 105, 122, 135

Offset

1,1

Comments

See A250293 for more information.

Links

Table of n, a(n) for n=1..19.

Formula

a(n) = primepi(A250293(n)). - Hugo Pfoertner, Feb 05 2021

Prog

(PARI) isok(k) = bigomega(1 + prod(j=1, k, prime(j))) == 2; \\ Michel Marcus, Mar 30 2019

Crossrefs

Cf. A001358 (semiprimes), A002110, A006862 (Euclid numbers), A250293.

Sequence in context: A337543 A047394 A184874 * A049721 A092115 A083966

Adjacent sequences: A085722 A085723 A085724 * A085726 A085727 A085728

Keyword

more,hard,nonn

Author

Jason Earls, Jul 20 2003

Extensions

More terms from David Wasserman, Feb 09 2005

a(14)=54 from Donovan Johnson, Feb 21 2008

Offset changed to 1 by Alois P. Heinz, Jul 02 2015

a(15) added by Daniel Suteu, Mar 30 2019

a(16)-a(18) using terms of A250293 from Hugo Pfoertner, Feb 05 2021

Missing 105 inserted by Sean A. Irvine, Mar 03 2023

Status

approved