This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A015019 #27 Aug 10 2025 02:40:45
%S A015019 1,1,-5,-155,28675,31857925,-212333070125,-8491411807368875,
%T A015019 2037471806119124711875,2933289072587326393069793125,
%U A015019 -25337824341236140066496699758578125,-1313212585969062194023540996089250607796875,408368279891017634352398087776483543777178681171875
%N A015019 q-factorial numbers for q=-6.
%H A015019 Vincenzo Librandi, <a href="/A015019/b015019.txt">Table of n, a(n) for n = 0..50</a>
%H A015019 <a href="/index/Fa#factorial">Index entries for sequences related to factorial numbers</a>.
%F A015019 a(n) = Product_{k=1..n} ((-6)^k - 1) / (-6 - 1).
%F A015019 a(1) = 1, a(n) = ((-6)^n - 1)*a(n-1)/(-7). - _Vincenzo Librandi_, Oct 26 2012
%F A015019 a(n) ~ (-1)^floor(n/2) * c * 6^(n*(n+1)/2) / 7^n, where c = Product_{k>=1} (1 - 1/(-6)^k) = 1.1387567153634922027... . - _Amiram Eldar_, Aug 09 2025
%t A015019 RecurrenceTable[{a[1]==1, a[n]==(((-6)^n - 1) * a[n-1])/(-7)}, a, {n, 15}] (* _Vincenzo Librandi_, Oct 26 2012 *)
%o A015019 (Magma) [n le 1 select 1 else ((-6)^n - 1)*Self(n-1)/(-7): n in [1..18]]; // _Vincenzo Librandi_, Oct 26 2012
%Y A015019 Column k=6 of A384454.
%Y A015019 Cf. A015005.
%K A015019 sign,easy
%O A015019 0,3
%A A015019 _Olivier Gérard_
%E A015019 a(0)=1 prepended by _Seiichi Manyama_, May 30 2025