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 A267803 #15 Sep 05 2025 01:01:29
%S A267803 1,1,7,13,19,31,43,61,85,97,121,151,175,211,241,271,313,349,385,439,
%T A267803 499,535,583,649,691,757,823,877,955,1027,1087,1159,1249,1321,1401,
%U A267803 1483,1561,1663,1765,1827,1945,2053,2133,2233,2347,2443,2563,2677,2779,2905
%N A267803 Number of unit hexagonal lattice cells (hexagon in the origin) enclosed by origin centered circle of radius n.
%H A267803 Nicolay Avilov, <a href="/A267803/a267803.jpg">Illustration of the first terms</a>
%F A267803 Limit_{n->oo} a(n)/(n^2) = 2*Pi/(3*sqrt(3)).
%Y A267803 Cf. A053458, A267710.
%Y A267803 Cf. A248897 (2*Pi/(3*sqrt(3))).
%K A267803 nonn,easy,changed
%O A267803 1,3
%A A267803 _Luca Petrone_, Jan 20 2016