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 A115410 #14 May 05 2025 03:54:15
%S A115410 1,55,349074740,7458911738724515315524082613205180,
%T A115410 159232823342755035454279356693126603659457648808279391910878167820461916066223383414616137125812767424153893199341493609630
%N A115410 Sequence of iterated sums of squares (1^2+2^2+3^2+...+n^2).
%C A115410 Can be understood as generalized iterated square pyramidal numbers. The growth of the sequence is bounded by O(n^3^n/3^(n/2)). This can be derived from the growth O(n^3/3) of the power two sum (1^2+2^2+3^2+...+n^2) by iteration.
%F A115410 Let T(n):=Sum_{k=1..n} k^2; we define a(1):=T(1), a(2):=T(T(2)) etc., a(n):=T(T(T(...(T(n))...))).
%e A115410 a(2) = T(T(2)) = T(5) = 55;
%e A115410 a(3) = T(T(T(3))) = T(T(14)) = T(1015) = 349074740.
%t A115410 t[n_]:=Sum[k^2,{k,n}];Table[Nest[t[#]&,n,n],{n,5}] (* _James C. McMahon_, Aug 10 2024 *)
%Y A115410 Cf. A000330, A099129.
%K A115410 nonn,easy
%O A115410 1,2
%A A115410 _Hieronymus Fischer_, Jan 22 2006