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 A274392 #5 Jun 24 2016 22:52:44
%S A274392 1,4,63,2056,112625,9266706,1067280319,163802295616,32300931452769,
%T A274392 7956776354536450,2394142654816299431,863996246301971667600,
%U A274392 368314015001746325448313,183100281424495288847092386,104989565698848905178879275775,68778360046311927838608116567296,51049027217135211093037275781929857,42614907995326324626989103964953188610,39750079580111447237206552931429888023399,41188867531604111691413161924808444678694800,47163303540183246052916530453746351377795346681
%N A274392 A diagonal of rectangular array A274390 of coefficients in the iterations of Euler's tree function (A000169).
%H A274392 Paul D. Hanna, <a href="/A274392/b274392.txt">Table of n, a(n) for n = 1..100</a>
%o A274392 (PARI) {ITERATE(F,n,k) = my(G=x +x*O(x^k)); for(i=1,n,G=subst(G,x,F));G}
%o A274392 {A274390(n,k) = my(TREE = serreverse(x*exp(-x +x*O(x^k)))); k!*polcoeff(ITERATE(TREE,n,k),k)}
%o A274392 /* Print A274390 */
%o A274392 for(n=0,10,for(k=1,10,print1(A274390(n,k),", "));print("..."))
%o A274392 /* Print this sequence, as a diagonal of A274390 */
%o A274392 for(n=1,20,print1(A274390(n,n),", "))
%Y A274392 Cf. A274390, A000169, A274389.
%K A274392 nonn
%O A274392 1,2
%A A274392 _Paul D. Hanna_, Jun 24 2016