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 A166458 #12 Feb 19 2021 01:53:15 %S A166458 1,2,3,6,7,8,13,14,15,18,19,20,21,24,25,27,31,33,36,38,42,43,44,48,49, %T A166458 50,57,60,62,63,66,69,72,74,75,81,84,86,91,92,97,99,102,103,104,105, %U A166458 109,115,117,123,126,128,129,132,140,144,145,146,147,150,151,153,156,157 %N A166458 Numbers k such that 10*k - (-1)^k is prime. %H A166458 G. C. Greubel, <a href="/A166458/b166458.txt">Table of n, a(n) for n = 1..10000</a> %e A166458 1*10 - (-1)^1 = 11 is prime, so 1 is a term; %e A166458 2*10 - (-1)^2 = 19 is prime, so 2 is a term; %e A166458 3*10 - (-1)^3 = 31 is prime, so 3 is a term; %e A166458 4*10 - (-1)^4 = 39 = 3*13, so 4 is not a term. %t A166458 Select[If[PrimeQ[10*# - (-1)^#], #] & /@ Range[6!], IntegerQ] (* _G. C. Greubel_, May 15 2016 *) %Y A166458 Cf. A122869. %K A166458 nonn,easy %O A166458 1,2 %A A166458 _Juri-Stepan Gerasimov_, Oct 14 2009 %E A166458 Corrected (77 removed) by _R. J. Mathar_, May 21 2010