A289501 Number of enriched p-trees of weight n.
1, 1, 2, 4, 12, 32, 112, 352, 1296, 4448, 16640, 59968, 231168, 856960, 3334400, 12679424, 49991424, 192890880, 767229952, 2998427648, 12015527936, 47438950400, 191117033472, 760625733632, 3082675150848, 12346305839104, 50223511928832, 202359539335168
Offset: 0
Keywords
Examples
The a(4) = 12 enriched p-trees are: 4, (31), ((21)1), (((11)1)1), ((111)1), (22), (2(11)), ((11)2), ((11)(11)), (211), ((11)11), (1111).
Links
- Alois P. Heinz, Table of n, a(n) for n = 0..1588
Programs
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Maple
b:= proc(n, i) option remember; `if`(n=0, 1, `if`(i<1, 0, b(n, i-1)+a(i)*b(n-i, min(n-i, i)))) end: a:= n-> `if`(n=0, 1, 1+b(n, n-1)): seq(a(n), n=0..30); # Alois P. Heinz, Jul 07 2017
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Mathematica
a[n_]:=a[n]=1+Sum[Times@@a/@y,{y,Rest[IntegerPartitions[n]]}]; Array[a,20] (* Second program: *) b[n_, i_] := b[n, i] = If[n == 0, 1, If[i<1, 0, b[n, i-1] + a[i] b[n-i, Min[n-i, i]]]]; a[n_] := If[n == 0, 1, 1 + b[n, n-1]]; a /@ Range[0, 30] (* Jean-François Alcover, May 09 2021, after Alois P. Heinz *)
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PARI
seq(n)={my(v=vector(n)); for(n=1, n, v[n] = 1 + polcoef(1/prod(k=1, n-1, 1 - v[k]*x^k + O(x*x^n)), n)); concat([1], v)} \\ Andrew Howroyd, Aug 26 2018
Formula
O.g.f.: (1/(1-x) + Product_{i>0} 1/(1-a(i)*x^i))/2.
Comments