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 A215804 #36 Jan 04 2022 21:57:19 %S A215804 1,5,7,13,19,25,29,31,35,43,53,61,65,67,71,95,125,145,155,175,179,215, %T A215804 239,263,265,269,293,305 %N A215804 Odd numbers k such that 10^k + 1 can be written in the form a^2 + 2*b^2. %C A215804 These 10^k + 1 numbers have no prime factors of the form 5 or 7 (mod 8) to an odd power. %H A215804 Samuel S. Wagstaff, Jr., The Cunningham Project, <a href="http://homes.cerias.purdue.edu/~ssw/cun/">Factorizations of 2^n-1, for odd n's < 1200</a> %o A215804 (PARI) for(i=2, 100, a=factorint(10^i+1)~; has=0; for(j=1, #a, if(a[1, j]%8>4&&a[2, j]%2==1, has=1; break)); if(has==0&&i%2==1, print(i" -\t"a[1, ]))) %Y A215804 Cf. A000533, A001562, A062397, A215805. %K A215804 nonn %O A215804 1,2 %A A215804 _V. Raman_, Aug 23 2012 %E A215804 12 more terms from _V. Raman_, Aug 28 2012