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 A309173 #5 Jul 15 2019 15:40:31
%S A309173 1,1,2,4,6,10,15,23,34,50,71,100,140,195,268,363,487,650,865,1145,
%T A309173 1505,1962,2541,3275,4208,5390,6879,8740,11053,13917,17459,21837,
%U A309173 27244,33906,42085,52085,64268,79071,97025,118772,145082,176869,215204,261333,316705,383019
%N A309173 Expansion of Product_{k>=1} (1 + (1 + x + x^2) * x^k).
%F A309173 G.f.: exp(Sum_{k>=1} x^k * Sum_{d|k} (-1)^(d+1) * (1 + x + x^2)^d/d).
%t A309173 nmax = 45; CoefficientList[Series[Product[(1 + (1 + x + x^2) x^k), {k, 1, nmax}], {x, 0, nmax}], x]
%t A309173 nmax = 45; CoefficientList[Series[Exp[Sum[x^k Sum[(-1)^(d + 1) (1 + x + x^2)^d/d, {d, Divisors[k]}], {k, 1, nmax}]], {x, 0, nmax}], x]
%Y A309173 Cf. A160571, A227681, A309172.
%K A309173 nonn
%O A309173 0,3
%A A309173 _Ilya Gutkovskiy_, Jul 15 2019