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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

Table of n, a(n) for n=1..9.

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.)