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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.
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
Sequence in context: A128496 A134955 A171887 * A002861 A032200 A130969
Adjacent sequences: A027878 A027879 A027880 * A027882 A027883 A027884
Dirk Kreimer (kreimer(AT)dipmza.physik.Uni-Mainz.DE)