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 A232437 #24 Feb 20 2020 06:58:07
%S A232437 7,13,14,19,21,26,28,31,35,37,38,39,42,43,52,56,57,61,62,63,65,67,70,
%T A232437 73,74,76,77,78,79,84,86,93,95,97,103,104,105,109,111,112,114,117,119,
%U A232437 122,124,126,127,129,130,134,139,140,143,146,148,151,152,154,155,156,157,158,161
%N A232437 Numbers whose square is expressible in only one way as x^2+xy+y^2, with x and y > 0.
%C A232437 Analog of A084645 for 120-degree angle triangles with integer sides.
%C A232437 Numbers with exactly one prime divisor of the form 6k+1 with multiplicity one.
%C A232437 Primitive elements of A050931.
%H A232437 Ray Chandler, <a href="/A232437/b232437.txt">Table of n, a(n) for n = 1..10000</a>
%H A232437 <a href="/index/Aa#A2">Index entries for sequences related to A2 = hexagonal = triangular lattice</a>
%F A232437 Terms are obtained by the products A230780(k)*A002476(p) for k, p > 0, ordered by increasing values.
%e A232437 a(1) = 7 as 7^2 = 3^2 + 3*5 + 5^2.
%t A232437 r[k_] := Reduce[x>0 && y>0 && k^2 == x^2 + x y + y^2, {x, y}, Integers];
%t A232437 selQ[k_] := Which[rk = r[k]; rk === False, False, rk[[0]] === And && Length[rk] == 2, False, rk[[0]] === Or && Length[rk] == 2, True, True, False];
%t A232437 Select[Range[1000], selQ] (* _Jean-François Alcover_, Feb 20 2020 *)
%Y A232437 Cf. A002476, A050931, A230780, A232436 (subsequence).
%Y A232437 Cf. A084645, A232437, A248599, A254063, A254064.
%K A232437 nonn
%O A232437 1,1
%A A232437 _Jean-Christophe Hervé_, Nov 24 2013