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 A331540 #7 Jan 20 2020 12:51:57 %S A331540 1,2,2,5,10,16,31,47,88,149,290,536,952,1769,3280,6186,11638,21901, %T A331540 41488,78543,149662,284735,543155,1040577,1994339,3834731,7373228, %U A331540 14206331,27405523,52941914,102381148 %N A331540 Number of primes of the form k*2^n + 1 with k < 2^n. %C A331540 Both even and odd k are counted. Variant of A134876. %o A331540 (PARI) a(n) = sum(k=1,2^n-1,ispseudoprime(k<<n+1)) %Y A331540 Cf. A134876. %K A331540 nonn,more %O A331540 1,2 %A A331540 _Jeppe Stig Nielsen_, Jan 19 2020