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 A089709 #9 Aug 25 2024 18:44:46
%S A089709 1,2,6,36,360,6480,220320,14541120,1890345600,487709164800,
%T A089709 250682510707200,257200255985587200,527260524770453760000,
%U A089709 2160713630509319508480000,17704887488393364052485120000
%N A089709 a(1) = 1, a(2) = 2; for n>2, a(n) = sum_{r=1..n} {sum of all previous terms taken r at a time}.
%F A089709 a(n)=(2^(n-2)+2)*a(n-1), n>3. - _Vladeta Jovovic_, Nov 17 2003
%e A089709 a(4) = [{a(1)} + {a(2)} + {a(3)}] + [{a(1) + a(2)} + {a(1) + a(3)} + {a(2) + a(3)}] + [{a(1) + a(2) + a(3)}] = 36.
%Y A089709 Cf. A089985.
%K A089709 nonn,easy
%O A089709 1,2
%A A089709 _Amarnath Murthy_, Nov 14 2003
%E A089709 More terms from _Ray Chandler_, Nov 21 2003