A015013 q-factorial numbers for q=-2.

1, -1, -3, 15, 165, -3465, -148995, 12664575, 2165642325, -738484032825, -504384594419475, 688484971382583375, 1880252456845835197125, -10268058666835106011499625, -112158004817839862963610403875

Offset

1,3

Links

Vincenzo Librandi, Table of n, a(n) for n = 1..80

Index entries for sequences related to factorial numbers

Formula

a(n) = Product_{k=1..n} ((-2)^k - 1) / (-2 - 1).

a(1) = 1, a(n) = (((-2)^n - 1) * a(n-1))/(-3). - Vincenzo Librandi, Oct 26 2012

a(n) = (-1)^(floor((n mod 4)/2)) * Product_{k=1..n} A001045(k). - Altug Alkan, Apr 05 2016

Mathematica

RecurrenceTable[{a[1]==1, a[n]==(((-2)^n - 1) * a[n-1])/(-3)}, a, {n, 15}]
Table[QFactorial[n, -2], {n, 20}] (* Vladimir Reshetnikov, Sep 16 2016 *)

Prog

(Magma) I:=[1]; [n le 1 select I[n] else (((-2)^n - 1) * Self(n-1))/(-3): n in [1..18]]; // Vincenzo Librandi, Oct 26 2012
(PARI) a(n) = prod(k=1, n, ((-2)^k-1)/(-3)) \\ Michel Marcus, Apr 05 2016

Crossrefs

Cf. A001045.

Sequence in context: A108975 A097489 A080696 * A269694 A153280 A132683

Adjacent sequences: A015010 A015011 A015012 * A015014 A015015 A015016

Keyword

sign,easy

Author

Olivier Gérard

Status

approved