A159333 Roman factorial of n.

-1, 1, 1, 1, 2, 6, 24, 120, 720, 5040, 40320, 362880, 3628800, 39916800, 479001600, 6227020800, 87178291200, 1307674368000, 20922789888000, 355687428096000, 6402373705728000, 121645100408832000, 2432902008176640000

Offset

-2,5

Links

G. C. Greubel, Table of n, a(n) for n = -2..100

Eric W. Weisstein, Roman Factorial.

Formula

a(n) = n! for n >=0 and ((-1)^(n + 1))/(-n - 1)! for n < 0.

Maple

A159333 := n -> ifelse(n < 0, (-1)^(-n - 1)/(-n - 1)!, n!):
seq(A159333(n), n = -2..9);  # Peter Luschny, Jun 11 2022

Mathematica

Table[If[n < 0, (-1)^(-n - 1)/(-n - 1)!, n!], {n, -2, 30}] (* G. C. Greubel, Jun 25 2018 *)

Prog

(PARI) for(n=-2, 30, print1(if(n<0, (-1)^(-n - 1)/(-n - 1)!, n!), ", ")) \\ G. C. Greubel, Jun 25 2018
(Magma) [-1, 1] cat [Factorial(n): n in [0..30]]; // G. C. Greubel, Jun 25 2018

Crossrefs

Cf. A000142.

Sequence in context: A155456 A124355 A133942 * A165233 A000142 A104150

Adjacent sequences: A159330 A159331 A159332 * A159334 A159335 A159336

Keyword

easy,sign,less

Author

Jonathan Vos Post, Apr 10 2009

Status

approved