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 A128811 #4 Mar 30 2012 18:40:42 %S A128811 1,4,35,240,3003,26880,415701,4435200,79676025,968647680,19535112675, %T A128811 263472168960,5837993287875,85816649318400,2058476433304725, %U A128811 32567418416332800,836589039864843825,14112547980410880000 %N A128811 A113551(n)/A006882(n). %C A128811 a(n) is to A001700 as n!! is to n!. %F A128811 a(n) = n * (n+2) * ... * ((3*n)-2) / n!!. %e A128811 a(1) = (1)/(1) = 1. %e A128811 a(2) = (2*4)/(2) = 4. %e A128811 a(3) = (3*5*7)/(3*1) = 35. %e A128811 a(4) = (4*6*8*10)/(4*2) = 240. %e A128811 a(5) = (5*7*9*11*13)/(5*3*1) = 3003. %e A128811 a(6) = (6*8*10*12*14*16)/(6*4*2) = 26880. %Y A128811 Cf. A001700, A006882, A113551. %K A128811 easy,nonn %O A128811 1,2 %A A128811 _Jonathan Vos Post_, Apr 10 2007 %E A128811 Corrected and extended by _Klaus Brockhaus_, Apr 15 2007