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 A260262 #16 Aug 29 2015 14:45:10
%S A260262 1,1,5,10703,1614696745,28812381422477890,100652205682053466439353073,
%T A260262 100862590668529143951825397261798321446,
%U A260262 39596172587764149886638486692811308322476202830248047,7942534398808419809836601901425429825855063583537701822391757140131840
%N A260262 Number of digits of hyperfactorial(hyperfactorial(n)).
%H A260262 Matthew Campbell, <a href="/A260262/b260262.txt">Table of n, a(n) for n = 0..27</a>
%F A260262 a(n) = floor(log_10(hyperfactorial(hyperfactorial(n))))+1.
%F A260262 a(n) = A055642(A002109(A002109(n))).
%e A260262 Hyperfactorial(Hyperfactorial(1)) = 1. There is 1 digit in the number 1. Because of this, a(1) = 1.
%t A260262 Table[Floor[Log[10, Hyperfactorial[Hyperfactorial[n]]]] + 1, {n, 0, 3}]
%o A260262 (PARI) hyperfactorial(n)=prod(k=2,n,k^k)
%o A260262 first(m)=vector(m,i,#digits(hyperfactorial(hyperfactorial(i)))) \\ _Anders Hellström_, Aug 29 2015
%Y A260262 Cf. A002109, A055642.
%K A260262 nonn,easy,base
%O A260262 0,3
%A A260262 _Matthew Campbell_, Jul 21 2015