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 A215801 #31 Jan 04 2022 21:52:02 %S A215801 3,7,13,19,31,37,43,61,67,73,79,109,127,139,151,199,277,313,433,457, %T A215801 547,613,619,643,739,967 %N A215801 Prime numbers p such that (2^p + 1)/3 can be written in the form a^2 + 3*b^2. %C A215801 These (2^p + 1)/3 numbers have no prime factors of the form 2 (mod 3) to an odd power. %H A215801 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 A215801 (PARI) forprime(i=2, 100, a=factorint(2^i+1)~; has=0; for(j=1, #a, if(a[1, j]%3==2&&a[2, j]%2==1, has=1; break)); if(has==0, print(i" -\t"a[1, ]))) %Y A215801 Cf. A000051, A000978, A215800. %K A215801 nonn %O A215801 1,1 %A A215801 _V. Raman_, Aug 23 2012 %E A215801 9 more terms from _V. Raman_, Aug 28 2012