110 people attended OEIS-50 (videos, suggestions); annual fundraising drive to start soon (donate); editors, please edit! (stack is over 300), your editing is more valuable than any donation.
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)