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 A087422 Number of terms in the expansion of Product(x_i + x_{i+1} + ... + x_j) over 1 <= i < j <= n. 2
 1, 2, 8, 55, 567, 7958, 142396, 3104160, 79813513 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS The sum of the coefficients in the expansion of this product are the superfactorials A000178. - Robert G. Wilson v, Aug 02 2005. LINKS EXAMPLE a(3)=8 because the expansion of (x+y)(y+z)(x+y+z) has 8 terms. MATHEMATICA 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 *) CROSSREFS Sequence in context: A183282 A139016 A134954 * A081667 A117496 A117564 Adjacent sequences:  A087419 A087420 A087421 * A087423 A087424 A087425 KEYWORD nonn AUTHOR Alex Postnikov (apost(AT)math.mit.edu), Oct 22 2003 EXTENSIONS a(8) from Robert G. Wilson v, Apr 26 2005 a(9) from Vaclav Kotesovec, Apr 09 2021 STATUS approved

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Last modified May 28 16:37 EDT 2022. Contains 354119 sequences. (Running on oeis4.)