A216733 a(1)=1; thereafter a(n) = (n/2)*Sum_{i=1..n-1} K(i,n-i)*a(i)*a(n-i), where K(i,j)=i/j+j/i+2.

1, 4, 54, 1280, 44500, 2095632, 127881376, 9819500544, 928097190000, 106056995000000, 14432021983025504, 2308065337772034048, 428863163196474895616, 91656939861553564825600, 22332165732277725605760000, 6154560612828089005182025728, 1905106896258617768240402396928, 658221263587332244069472967367680, 252407458471654722567803941053452800

Offset

1,2

Links

Table of n, a(n) for n=1..19.

P. L. Krapivsky and Colm Connaughton, Driven Brownian coagulation of polymers, arXiv preprint arXiv:1203.3905, 2012

Maple

K:=(i, j)->i/j+j/i+2;
B:=proc(n) option remember; global K;
if n=1 then 1 else
(n/2)*add( K(i, n-i)*B(i)*B(n-i), i=1..n-1); fi; end;

Mathematica

K[i_, j_] := i/j + j/i + 2;
a[1] = 1; a[n_] := a[n] = (n/2) Sum[K[i, n-i] a[i] a[n-i], {i, 1, n-1}];
Array[a, 19] (* Jean-François Alcover, Dec 06 2017 *)

Crossrefs

Sequence in context: A259063 A138459 A111161 * A203039 A369569 A201731

Adjacent sequences: A216730 A216731 A216732 * A216734 A216735 A216736

Keyword

nonn

Author

N. J. A. Sloane, Sep 17 2012

Status

approved