This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A364840 #9 Oct 21 2023 17:11:08 %S A364840 4,7,10,11,14,17,20,21,25,26,48,51,55,85,96,127,149,150,170 %N A364840 Numbers k such that the product of the first k primes - 1 is a semiprime. %F A364840 a(n) = primepi(A104876(n)). %o A364840 (PARI) isok(k) = bigomega(-1 + prod(j=1, k, prime(j))) == 2; %Y A364840 Cf. A000720, A057588, A001358, A104876, A085725, A057704. %K A364840 more,hard,nonn %O A364840 1,1 %A A364840 _Sean A. Irvine_, Oct 21 2023