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 A308685 #32 Apr 08 2022 04:03:28 %S A308685 1,7,19,37,61,91,127,187,241,301,367,439,517,613,721,823,931,1045, %T A308685 1165,1303,1459,1615,1765,1921,2083,2263,2455,2653,2857,3055,3259, %U A308685 3481,3697,3949,4195,4447,4693,4957,5239,5527,5815,6109,6409,6715,7015,7333,7681 %N A308685 The number of triangular lattice points whose Euclidean distance from the origin is less than or equal to n. %C A308685 Also the sum of the first n^2+1 terms of A004016. %H A308685 Peter Kagey, <a href="/A308685/b308685.txt">Table of n, a(n) for n = 0..1000</a> %H A308685 Code Golf Stack Exchange, <a href="https://codegolf.stackexchange.com/q/163704">Triangular Lattice Points close to the Origin</a> %F A308685 a(n) = A053416(2*n). %o A308685 (PARI) a(n)=1+2*vecsum(Vec(qfrep([2,1;1,2],n^2,1))) /* _Georg Fischer_, Apr 07 2022 (from codegolf link) */ %Y A308685 Cf. A004016, A053416. %K A308685 nonn %O A308685 0,2 %A A308685 _Peter Kagey_, Jun 28 2019