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 A175421 #14 Feb 25 2024 10:21:11
%S A175421 0,1,2,3,4,5,6,7,8,9,0,1,2,3,4,5,6,7,8,9,0,1,4,9,6,25,216,6561,4096,1,
%T A175421 0,1,8,49,4096,25,36,531441,32,22876792454961,0,1,6,1,60466176,
%U A175421 244140625,101559956668416,1,1,1,0
%N A175421 Sequence of numbers after 2nd step of iteration defined in A175419.
%e A175421 For n = 33: a(33) = 49 because for the number 33 there are 4 steps of defined iteration: {3^3 = 27}, {7^2 = 49}, {9^4 = 6561}, {((1^6)^5)^6 = 1} and the 2nd step of the iteration ends with 49.
%t A175421 Unprotect[Power]; Power[0, 0] = 1; Protect[Power]; A175420[0]=0; A175420[n_]:=If[(len=IntegerLength[n])==1, n, Last[list=IntegerDigits[n]]^Product[Part[Drop[list, -1], i], {i, len-1}]]; a[n_]:=A175420[A175420[n]]; Array[a, 51, 0] (* _Stefano Spezia_, Feb 25 2024 *)
%Y A175421 Cf. A175419, A175420, A175422, A175423, A175424, A175425, A175426, A175427.
%K A175421 nonn,base
%O A175421 0,3
%A A175421 _Jaroslav Krizek_, May 09 2010