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A364840
Numbers k such that the product of the first k primes - 1 is a semiprime.
0
4, 7, 10, 11, 14, 17, 20, 21, 25, 26, 48, 51, 55, 85, 96, 127, 149, 150, 170
OFFSET
1,1
FORMULA
a(n) = primepi(A104876(n)).
PROG
(PARI) isok(k) = bigomega(-1 + prod(j=1, k, prime(j))) == 2;
CROSSREFS
KEYWORD
more,hard,nonn
AUTHOR
Sean A. Irvine, Oct 21 2023
STATUS
approved