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 A356516 #7 Aug 12 2022 12:37:26
%S A356516 0,1,3,31,9007199254740991
%N A356516 a(n) is the least k such that A356515(k) = n.
%C A356516 All terms belong to A000225.
%C A356516 a(5) = 2^1235346792567893 - 1 is too large to fit in the data section or in a b-file.
%F A356516 a(n) = A356517(2, A356517(3, ... A356517(n, n) ...)) for n > 1.
%e A356516 For n = 4:
%e A356516 - A356517(4, 4) = 7,
%e A356516 - A356517(3, 7) = 53,
%e A356516 - A356517(2, 53) = 9007199254740991,
%e A356516 - so a(4) = 9007199254740991.
%o A356516 (PARI) A356517(n, k) = { (1+k%(n-1))*n^(k\(n-1))-1 }
%o A356516 a(n) = { my (v=n); forstep (b=n, 2, -1, v=A356517(b,v)); v }
%Y A356516 Cf. A000225, A356515, A356517.
%K A356516 nonn,base,bref
%O A356516 0,3
%A A356516 _Rémy Sigrist_, Aug 10 2022