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 A274389 #9 Jun 24 2016 22:43:49
%S A274389 1,2,30,948,50680,4090980,463975764,70311813880,13718193268896,
%T A274389 3348658563980040,999698412743754460,358297471515195652308,
%U A274389 151813934699349280088328,75064081768759279536110316,42833194538353991390132088540,27937122503026656234469859408880,20653210428143999114034181337343616,17178393944175652034128269331788145680,15970217696130529428248774113884778921452,16497536217367322285994072192399435877530380,18836957575278690757486149667782477659475272520
%N A274389 Main diagonal of rectangular array A274390 of coefficients in the iterations of Euler's tree function (A000169).
%H A274389 Paul D. Hanna, <a href="/A274389/b274389.txt">Table of n, a(n) for n = 0..100</a>
%o A274389 (PARI) {ITERATE(F,n,k) = my(G=x +x*O(x^k)); for(i=1,n,G=subst(G,x,F));G}
%o A274389 {A274390(n,k) = my(TREE = serreverse(x*exp(-x +x*O(x^k)))); k!*polcoeff(ITERATE(TREE,n,k),k)}
%o A274389 /* Print A274390 */
%o A274389 for(n=0,10,for(k=1,10,print1(A274390(n,k),", "));print("..."))
%o A274389 /* Print this sequence, as the main diagonal of A274390 */
%o A274389 for(n=0,20,print1(A274390(n,n+1),", "))
%Y A274389 Cf. A274390, A000169, A274392.
%K A274389 nonn
%O A274389 0,2
%A A274389 _Paul D. Hanna_, Jun 24 2016