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 A138738 #6 Aug 08 2014 12:36:30
%S A138738 1,1,1,7,25,121,1561,9871,101137,1293265,15765841,226501111,
%T A138738 3355388521,55348183177,981791212585,19611613003711,387083895223201,
%U A138738 8241127257050401,193814428658623777,4572332597344204135,116627907470591924281,3142752742361513926681
%N A138738 E.g.f. satisfies: A(x) = exp(x*exp(x^2*exp(x^3*exp(...exp(x^n*...))))).
%C A138738 a(n) == 1 (mod 6) (conjecture).
%H A138738 Paul D. Hanna, <a href="/A138738/b138738.txt">Table of n, a(n) for n = 0..400</a>
%e A138738 E.g.f: A(x) = 1 + x + 1/2*x^2 + 7/6*x^3 + 25/24*x^4 + 121/120*x^5 +...
%o A138738 (PARI) {a(n)=local(A=1); for(i=0, n-1, A=exp(x^(n-i)*A+x*O(x^n))); n!*polcoeff(A, n)}
%o A138738 for(n=0,30,print1(a(n),", "))
%Y A138738 Cf. A138292.
%K A138738 nonn
%O A138738 0,4
%A A138738 _Paul D. Hanna_, Mar 27 2008