1,2

The sum of the coefficients in the expansion of this product are the superfactorials A000178. - Robert G. Wilson v (rgwv(AT)rgwv.com), Aug 02 2005.

a(3)=8 because the expansion of (x+y)(y+z)(x+y+z) has 8 terms.

f[1]=1; f[n_] := Block[{lst = Take[{a, b, c, d, e, f, g, h, i}, n], s = 1}, Do[s = s*Times @@ Plus @@@ Partition[lst, i, 1], {i, 2, n}]; Length@Expand@s]; Do[ Print@ f@n, {n, 9}] (* Robert G. Wilson v Sep 18 2006 *)

Sequence in context: A005440 A139016 A134954 this_sequence A081667 A117496 A117564

Adjacent sequences: A087419 A087420 A087421 this_sequence A087423 A087424 A087425

nonn

Alex Postnikov (apost(AT)math.mit.edu), Oct 22 2003

a(8) from Robert G. Wilson v (rgwv(AT)rgwv.com), Apr 26 2005