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 A261514 #17 Nov 25 2015 02:24:07 %S A261514 0,1,2,3,5,6,7,9,13,14,15,17,18,19,21,25,26,27,31,37,38,39,42,45,49, %T A261514 51,54,57,61,62,63,65,67,74,75,78,81,85,89,93,98,101,103,107,111,114, %U A261514 117,122,125,126,127,133,134,135,139,147,153,162,171,183,186,189,195 %N A261514 Indices of Mersenne numbers (A000225) of the form x^2 + xy + y^2. %C A261514 Inspired by intersection of nice and core sequences. Initial Mersenne numbers of the form x^2 + xy + y^2 are 0, 1, 3, 7, 31, 63, 127, 511, 8191, 16383. %e A261514 a(4) = 3 because 2^3 - 1 = 1^2 + 1*2 + 2^2 = 7. %e A261514 a(5) = 5 because 2^5 - 1 = 1^2 + 1*5 + 5^2 = 31. %o A261514 (PARI) is(n)=#bnfisintnorm(bnfinit(z^2+z+1), 2^n-1); %o A261514 for(n=0, 200, if(n==0 || is(n), print1(n, ", "))) %Y A261514 Cf. A000225, A003136. %K A261514 nonn %O A261514 1,3 %A A261514 _Altug Alkan_, Nov 18 2015