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%I #24 Dec 26 2023 11:16:05
%S -1,1,1,1,2,6,24,120,720,5040,40320,362880,3628800,39916800,479001600,
%T 6227020800,87178291200,1307674368000,20922789888000,355687428096000,
%U 6402373705728000,121645100408832000,2432902008176640000
%N Roman factorial of n.
%H G. C. Greubel, <a href="/A159333/b159333.txt">Table of n, a(n) for n = -2..100</a>
%H Eric W. Weisstein, <a href="http://mathworld.wolfram.com/RomanFactorial.html">Roman Factorial.</a>
%F a(n) = n! for n >=0 and ((-1)^(n + 1))/(-n - 1)! for n < 0.
%p A159333 := n -> ifelse(n < 0, (-1)^(-n - 1)/(-n - 1)!, n!):
%p seq(A159333(n), n = -2..9); # _Peter Luschny_, Jun 11 2022
%t Table[If[n < 0, (-1)^(-n - 1)/(-n - 1)!, n!], {n, -2, 30}] (* _G. C. Greubel_, Jun 25 2018 *)
%o (PARI) for(n=-2, 30, print1(if(n<0, (-1)^(-n - 1)/(-n - 1)!, n!), ", ")) \\ _G. C. Greubel_, Jun 25 2018
%o (Magma) [-1,1] cat [Factorial(n): n in [0..30]]; // _G. C. Greubel_, Jun 25 2018
%Y Cf. A000142.
%K easy,sign,less
%O -2,5
%A _Jonathan Vos Post_, Apr 10 2009
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