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 A304491 #9 Aug 26 2018 18:41:31
%S A304491 1,2,3,2,5,6,7,3,2,10,11,12,13,14,15,2,17,18,19,20,21,22,23,24,2,26,3,
%T A304491 28,29,30,31,5,33,34,35,2,37,38,39,40,41,42,43,44,45,46,47,48,2,50,51,
%U A304491 52,53,54,55,56,57,58,59,60,61,62,63,6,65,66,67,68,69
%N A304491 Last or deepest exponent in the power-tower for n.
%C A304491 Let {c(i)} = A007916 denote the sequence of numbers > 1 which are not perfect powers. Every positive integer n has a unique representation as a tower n = c(x_1)^c(x_2)^c(x_3)^...^c(x_k), where the exponents are nested from the right. Then a(n) = c(x_k).
%H A304491 Andrew Howroyd, <a href="/A304491/b304491.txt">Table of n, a(n) for n = 1..10000</a>
%F A304491 a(n) = A007916(A278028(n, A288636(n))).
%e A304491 We have 16 = 2^2^2, so a(16) = 2.
%e A304491 We have 64 = 2^6, so a(64) = 6.
%e A304491 We have 81 = 3^2^2, so a(81) = 2.
%e A304491 We have 256 = 2^2^3, so a(256) = 3.
%t A304491 a[n_]:=If[n==1,1,With[{g=GCD@@FactorInteger[n][[All,2]]},If[g==1,n,a[g]]]];
%t A304491 Array[a,100]
%o A304491 (PARI) a(n)={my(t=n); while(t, n=t; t=ispower(t)); n} \\ _Andrew Howroyd_, Aug 26 2018
%Y A304491 Cf. A052409, A052410, A007916, A089723, A164337, A277562, A277564, A278028, A288636, A289023, A294336, A294337, A304481, A304492, A304495.
%K A304491 nonn
%O A304491 1,2
%A A304491 _Gus Wiseman_, May 13 2018