A015023 - OEIS

%I #12 Sep 08 2022 08:44:39

%S 1,-8,-584,383104,2262229120,-120223904353280,-57502732780460764160,

%T 247530403723531598578155520,9589835030046843645163231485460480,

%U -3343768718134086569119429099709242848051200

%N q-factorial numbers for q=-9.

%H Vincenzo Librandi, <a href="/A015023/b015023.txt">Table of n, a(n) for n = 1..40</a>

%H <a href="/index/Fa#factorial">Index entries for sequences related to factorial numbers</a>

%F prod_{k=1}^{k=n} {(q^k - 1) / (q - 1)}

%F a(1) = 1, a(n) = (((-9)^n - 1) * a(n-1))/(-10). - _Vincenzo Librandi_, Oct 26 2012

%t RecurrenceTable[{a[1]==1, a[n]==(((-9)^n - 1) * a[n-1])/(-10)}, a, {n, 15}] (* _Vincenzo Librandi_, Oct 26 2012 *)

%o (Magma) I:=[1]; [n le 1 select I[n] else (((-9)^n - 1) * Self(n-1))/(-10): n in [1..13]]; // _Vincenzo Librandi_, Oct 26 2012

%K sign,easy

%O 1,2

%A _Olivier Gérard_