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%I #24 Apr 24 2018 02:12:12
%S 0,1,5,20,0,-1560,-26825,-272000,0,84086080,2484885325,40560998400,0,
%T -28152429760000,-1180588763732625,-26582971351040000,0,
%U 32774236110420480000,1780605230870046303125,51128938217766256640000,0,-98456230888859903488000000,-6569779608356896665959265625
%N Imaginary part of Product_{k=1..n} (k+(n-k+1)i), with i=sqrt(-1).
%C a(n) = 0 when n is a multiple of 4 (A008586). - _Michel Marcus_, Apr 11 2018
%H Seiichi Manyama, <a href="/A302662/b302662.txt">Table of n, a(n) for n = 0..398</a>
%p seq(Im(mul(k+(n-k+1)*I,k=1..n)),n=0..30); # _Muniru A Asiru_, Apr 11 2018
%o (PARI) {a(n) = imag(prod(k=1, n, k+(n-k+1)*I))}
%Y Cf. A008586, A301616.
%Y Real part: A302661.
%K sign
%O 0,3
%A _Seiichi Manyama_, Apr 11 2018