A007098 Number of unlabeled bisectable trees with 2n+1 nodes.

1, 1, 3, 6, 19, 47, 140, 374, 1082, 2998, 8574, 24130, 68876, 195587, 559076, 1596651, 4575978, 13122219, 37711998, 108488765, 312577827, 901531937, 2603264050, 7524331268, 21768850808, 63032844756, 182662328945, 529722408615, 1537261773438

Offset: 0

Author

N. J. A. Sloane, Mira Bernstein

Keywords

• nonn

References

• R. W. Robinson, Numerical implementation of graph counting algorithms, AGRC Grant, Math. Dept., Univ. Newcastle, Australia, 1980.
• N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

Links

• R. W. Robinson, Table of n, a(n) for n = 0..99
• F. Harary, R. W. Robinson, Isomorphic factorizations VIII: bisectable trees, Combinatorica 4 (2) (1984) 169-179.
• Index entries for sequences related to trees

Crossrefs

Cf. A228601.

Formula

a(n) = Sum_{k=1..n} binomial(k + 1, 2) * A228601(n, k). - Sean A. Irvine, Oct 10 2017

Extensions

a(23) onwards added by N. J. A. Sloane, Oct 19 2006 from the Robinson reference