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 A175131 #19 Jun 27 2024 09:01:38
%S A175131 1,2,4,8,2,2,1,18,6,18,1,8,1,22,4,16,23,2,14,2,52,2,49,2,10,65,64,8,
%T A175131 44,2,64,2,42,12,62,56,31,98,81,50,74,2,1,128,96,71,60,7,81,16,94,146,
%U A175131 1,144,108,154,133,4,46,153,67,44,88,90,198,32,14,117
%N A175131 a(n) = 2^(n-1) mod semiprime(n).
%H A175131 Harvey P. Dale, <a href="/A175131/b175131.txt">Table of n, a(n) for n = 1..1000</a>
%t A175131 Module[{nn=300,sems,len},sems=Select[Range[nn],PrimeOmega[#]==2&];len = Length[sems];PowerMod[2,#[[1]]-1,#[[2]]]&/@Thread[{Range[len],sems}]] (* _Harvey P. Dale_, May 19 2018 *)
%o A175131 (PARI) lista(nn) = {semip = select(n->bigomega(n) == 2, vector(nn, i, i)); for (i=1, #semip, print1(2^(i-1) % semip[i], ", "););} \\ _Michel Marcus_, Sep 11 2013
%Y A175131 Cf. A000079, A001358, A175036, A181615.
%K A175131 nonn,less
%O A175131 1,2
%A A175131 _Juri-Stepan Gerasimov_, Dec 02 2010
%E A175131 More terms from _Michel Marcus_, Sep 11 2013