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
Programs
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PARI
isok(k) = bigomega(1 + prod(j=1, k, prime(j))) == 2; \\ Michel Marcus, Mar 30 2019
Formula
a(n) = primepi(A250293(n)). - Hugo Pfoertner, Feb 05 2021
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
Comments