A364840 Numbers k such that the product of the first k primes - 1 is a semiprime.

4, 7, 10, 11, 14, 17, 20, 21, 25, 26, 48, 51, 55, 85, 96, 127, 149, 150, 170

Offset

1,1

Links

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

Formula

a(n) = primepi(A104876(n)).

Prog

(PARI) isok(k) = bigomega(-1 + prod(j=1, k, prime(j))) == 2;

Crossrefs

Cf. A000720, A057588, A001358, A104876, A085725, A057704.

Sequence in context: A275340 A082206 A115566 * A190507 A087298 A237707

Adjacent sequences: A364837 A364838 A364839 * A364841 A364842 A364843

Keyword

more,hard,nonn

Author

Sean A. Irvine, Oct 21 2023

Status

approved