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 A015004 #36 Jul 06 2025 10:11:53
%S A015004 1,1,6,186,29016,22661496,88515803376,1728802155736656,
%T A015004 168827903320618878336,82435457461295106532780416,
%U A015004 201258420458750640859769304304896,2456767777551003294245070550498298923776,149949204558598784020761783280669552547300269056
%N A015004 q-factorial numbers for q=5.
%H A015004 Vincenzo Librandi, <a href="/A015004/b015004.txt">Table of n, a(n) for n = 0..50</a>
%H A015004 <a href="/index/Fa#factorial">Index entries for sequences related to factorial numbers</a>.
%F A015004 a(n) = Product_{k=1..n} ((q^k - 1) / (q - 1)) where q = 5.
%F A015004 a(0) = 1, a(n) = (5^n-1)*a(n-1)/4. - _Vincenzo Librandi_, Oct 25 2012
%F A015004 From _Amiram Eldar_, Jul 05 2025: (Start)
%F A015004 a(n) = Product_{k=1..n} A003463(k).
%F A015004 a(n) ~ c * 5^(n*(n+1)/2)/4^n, where c = A100222. (End)
%t A015004 RecurrenceTable[{a[1]==1, a[n]==((5^n - 1)* a[n-1])/4}, a, {n, 15}] (* _Vincenzo Librandi_, Oct 25 2012 *)
%t A015004 Table[QFactorial[n, 5], {n, 15}] (* _Bruno Berselli_, Aug 14 2013 *)
%o A015004 (Magma) [n le 1 select 1 else (5^n-1)*Self(n-1)/4: n in [1..15]]; // _Vincenzo Librandi_, Oct 25 2012
%o A015004 (PARI) a(n) = { my(q=5); prod(k=1, n, ((q^k - 1) / (q - 1))) } \\ _Andrew Howroyd_, Feb 18 2018
%Y A015004 Column q=5 of A069777.
%Y A015004 Cf. A015001, A015002, A015005, A015006, A015007, A015008, A015009, A015011.
%Y A015004 Cf. A003463, A100222.
%K A015004 nonn,easy
%O A015004 0,3
%A A015004 _Olivier Gérard_
%E A015004 a(0)=1 prepended by _Alois P. Heinz_, Sep 08 2021