

A105751


Imaginary part of Product_{k=0..n} 1+k*I, I=sqrt(1).


2



0, 1, 3, 0, 40, 90, 1050, 6160, 46800, 549900, 3103100, 67610400, 271627200, 11186357000, 26495469000, 2416003824000, 1394099824000, 662595375078000, 936096296850000, 225382826562400000, 819329864480400000, 93217812901913700000, 570263312237604700000
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OFFSET

0,3


LINKS

Seiichi Manyama, Table of n, a(n) for n = 0..450


FORMULA

a(n) = ((2*n1)*a(n1)(n^22*n+2)*n*a(n2))/(n1) for n > 1, a(n) = n for n < 2.  Alois P. Heinz, Apr 11 2018


MAPLE

a:= proc(n) option remember; `if`(n<2, n,
((2*n1)*a(n1)(n^22*n+2)*n*a(n2))/(n1))
end:
seq(a(n), n=0..25); # Alois P. Heinz, Apr 11 2018


PROG

(PARI) a(n) = imag(prod(k=0, n, 1+k*I)); \\ Michel Marcus, Apr 11 2018


CROSSREFS

Cf. A003703, A009454, A105750, A231531.
Sequence in context: A157310 A172396 A164806 * A177698 A009786 A012738
Adjacent sequences: A105748 A105749 A105750 * A105752 A105753 A105754


KEYWORD

easy,sign


AUTHOR

Paul Barry, Apr 18 2005


STATUS

approved



