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 A071109 #18 Apr 13 2018 21:52:31
%S A071109 1,-2,2,-6,14,-26,50,-102,214,-426,834,-1678,3398,-6778,13482,-27022,
%T A071109 54198,-108306,216346,-432878,866334,-1732386,3463626,-6927926,
%U A071109 13858350,-27715378,55426002,-110855030,221719582,-443433610,886848930,-1773709078,3547455846
%N A071109 Expansion of Product_{k>=1} 1/(1+2*x^k).
%H A071109 Vaclav Kotesovec, <a href="/A071109/b071109.txt">Table of n, a(n) for n = 0..2000</a>
%F A071109 a(n) ~ c * (-2)^n, where c = Product_{j>=1} 1/(1-1/(-2)^j) = 1/QPochhammer[-1/2,-1/2] = 0.8259519860658427384636116224100201356301... . - _Vaclav Kotesovec_, Aug 25 2015
%F A071109 G.f.: Sum_{i>=0} (-2)^i*x^i/Product_{j=1..i} (1 - x^j). - _Ilya Gutkovskiy_, Apr 13 2018
%t A071109 nmax = 40; CoefficientList[Series[Product[1/(1 + 2*x^k), {k, 1, nmax}], {x, 0, nmax}], x] (* _Vaclav Kotesovec_, Aug 25 2015 *)
%t A071109 nmax = 40; CoefficientList[Series[Exp[Sum[(-1)^k*2^k/k*x^k/(1-x^k), {k, 1, nmax}]], {x, 0, nmax}], x] (* _Vaclav Kotesovec_, Aug 25 2015 *)
%t A071109 (O[x]^30 + 3/QPochhammer[-2, x])[[3]] (* _Vladimir Reshetnikov_, Nov 20 2015 *)
%Y A071109 Cf. A070933, A032302, A000700, A246935, A261562, A261566, A261582.
%K A071109 sign
%O A071109 0,2
%A A071109 Sharon Sela (sharonsela(AT)hotmail.com), May 27 2002
%E A071109 More terms from _Vaclav Kotesovec_, Aug 25 2015