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A006706
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Self-convolution of numbers of trees on n nodes.
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1
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1, 2, 3, 4, 7, 12, 23, 44, 90, 186, 407, 902, 2072, 4844, 11595, 28150, 69491, 173522, 438423, 1117968, 2875960, 7453070, 19447591, 51050224, 134749849, 357446716, 952527403, 2548897192, 6846986075, 18458150242, 49923931099, 135443922536, 368511905808
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OFFSET
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0,2
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LINKS
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FORMULA
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a(n) ~ c * d^n / n^(5/2), where d = A051491 = 2.9557652856519949747148175..., c = 1.67518821170655279423478... . - Vaclav Kotesovec, Aug 25 2014
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MAPLE
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with(numtheory): b:= proc(n) option remember; local d, j; if n<=1 then n else (add(add(d*b(d), d=divisors(j)) *b(n-j), j=1..n-1))/ (n-1) fi end: t:= proc(n) option remember; local k; `if`(n=0, 1, b(n)- (add(b(k) *b(n-k), k=1..n-1) -`if`(type(n, odd), 0, b(n/2)))/2) end: a:= n-> add(t(j)* t(n-j), j=0..n): seq(a(n), n=0..40); # Alois P. Heinz, Oct 28 2008
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MATHEMATICA
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b[n_] := b[n] = If[n <= 1, n, (Sum[Sum[d*b[d], {d, Divisors[j]}]*b[n-j], {j, 1, n-1}])/(n-1)]; t[n_] := t[n] = If[n == 0, 1, b[n] - (Sum [b[k]*b[n-k], {k, 1, n-1}] - If[OddQ[n], 0, b[n/2]])/2]; a[n_] := Sum[t[j]*t[n-j], {j, 0, n}]; Table[a[n], {n, 0, 40}] (* Jean-François Alcover, Apr 28 2014, after Alois P. Heinz *)
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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