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A027881 a(i)=a(i-1)+a(j_1)*a(j_2) {where j_1+j_2=i-1, j_1 <= q j_2} + a(j_1)*a(j_2)*a(j_3) {where j_1+j_2+j_3=i-1, j_1 <= q j_2 <= q j_3} +...+ a(1)^{i-1}. 0
1, 1, 2, 4, 9, 20, 51, 121, 321, 826, 2186, 5789, 16114, 42449, 118281, 328425, 908933, 2510553, 7138324, 19869748 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

COMMENTS

At one time it was thought that this might be related to the Hopf algebra structure of perturbative Quantum Field Theory; this later proved not to be the case.

LINKS

Table of n, a(n) for n=1..20.

Dirk Kreimer, "On the Hopf algebra structure of perturbative quantum field theory"

Dirk Kreimer, Home page

CROSSREFS

Sequence in context: A128496 A134955 A171887 * A002861 A032200 A130969

Adjacent sequences:  A027878 A027879 A027880 * A027882 A027883 A027884

KEYWORD

nonn

AUTHOR

Dirk Kreimer (kreimer(AT)dipmza.physik.Uni-Mainz.DE)

STATUS

approved

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Last modified December 20 13:02 EST 2014. Contains 252257 sequences.