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 A256020 #11 Aug 04 2025 11:56:06
%S A256020 1,1,17,1394,358258,224269508,290877551876,698687879606152,
%T A256020 2862524242746404744,18783884080901907930128,
%U A256020 187857624693099981209210128,2750611340756369924865254694176,57039427373264843131930786593127712,1629160124635190449534207126672913710144
%N A256020 a(n) = Sum_{i=1..n-1} (i^4 * a(i)), a(1)=1.
%F A256020 a(n) = Product_{i=2..n-1} (i^4 + 1), for n>2.
%F A256020 a(n) ~ (cosh(Pi/sqrt(2))^2 * sin(Pi/sqrt(2))^2 + cos(Pi/sqrt(2))^2 * sinh(Pi/sqrt(2))^2) / (2*Pi^2) * ((n-1)!)^4.
%F A256020 a(n) = A255434(n-1)/2.
%t A256020 Clear[a]; a[1]=1; a[n_]:= a[n] = Sum[i^4*a[i],{i,1,n-1}]; Table[a[n],{n,1,15}]
%t A256020 Flatten[{1,1, Table[Product[(i^4 + 1), {i,2,n-1}],{n,3,15}]}]
%t A256020 Join[{1},FoldList[Times,Range[15]^4+1]/2] (* _Harvey P. Dale_, Jul 29 2018 *)
%Y A256020 Cf. A001710, A051893, A255434, A256019.
%K A256020 nonn
%O A256020 1,3
%A A256020 _Vaclav Kotesovec_, Mar 13 2015