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 A242666 #16 Jan 17 2023 03:32:49
%S A242666 0,3,6,7,12,14,19,24,27,28,31,38,47,48,54,56,59,62,63,75,76,83,87,94,
%T A242666 96,103,108,111,112,118,124,126,131,139,147,150,152,159,166,167,171,
%U A242666 174,175,188,192,199,203,206,216,222,223,224,227,236,243,248,251,252,259,262,271,278,279,283,294,300
%N A242666 Nonnegative integers of the form -x^2 + 4xy + 3y^2.
%C A242666 Discriminant 28.
%C A242666 Nonnegative numbers of the form 7x^2 - y^2. - _Jon E. Schoenfield_, Jun 03 2022
%C A242666 For the subsequence of the numbers with proper representations (gcd(x, y) = 1) see A359476. ~ _Wolfdieter Lang_, Jan 17 2023
%H A242666 N. J. A. Sloane et al., <a href="https://oeis.org/wiki/Binary_Quadratic_Forms_and_OEIS">Binary Quadratic Forms and OEIS</a> (Index to related sequences, programs, references)
%t A242666 Reap[For[n = 0, n <= 300, n++, If[Reduce[-x^2 + 4*x*y + 3*y^2 == n, {x, y}, Integers] =!= False, Sow[n]]]][[2, 1]]
%Y A242666 Primes in this sequence = A141173.
%Y A242666 Cf. A242662, A359476.
%K A242666 nonn
%O A242666 1,2
%A A242666 _N. J. A. Sloane_, May 31 2014