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a(n) = [x^n] 1 + x*(1 + x^2*(1 + x^3*(1 + x^4*(1 + x^5*(1 + ...)^n)^n)^n)^n)^n.
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%I #5 Apr 12 2018 05:15:17

%S 1,1,0,3,0,10,36,35,448,450,4600,13167,45408,240006,670124,3863835,

%T 13209088,60533974,268324056,1089776654,5328589520,22065836226,

%U 106289169448,481033496803,2231768294208,10748702587800,49858509230920,245664498591891,1175943617623264

%N a(n) = [x^n] 1 + x*(1 + x^2*(1 + x^3*(1 + x^4*(1 + x^5*(1 + ...)^n)^n)^n)^n)^n.

%t Table[SeriesCoefficient[1 + x Fold[(x^(#2 + 1) #1 + 1)^n &, 0, Reverse[Range[n]]], {x, 0, n}], {n, 0, 28}]

%Y Cf. A010054, A108643, A132330, A302657, A302686.

%K nonn

%O 0,4

%A _Ilya Gutkovskiy_, Apr 11 2018