A063689 Number of 2-trees rooted at a triangle with 3 similar edges.

1, 1, 2, 6, 21, 83, 356, 1599, 7434, 35381, 171508, 843419, 4197179, 21094355, 106915928, 545859112, 2804656069, 14491370996, 75248398034, 392476363133, 2055245992376, 10801442696736, 56953957110855, 301207378815752, 1597342159296786, 8492297139795170

Offset

1,3

References

F. Harary and E. M. Palmer, Graphical Enumeration, Academic Press, NY, 1973, p. 76, Eq. (3.5.17).

Links

Table of n, a(n) for n=1..26.

Formula

a(n) = A058870(n) + A063687(n) with A058870(0)=0. - Sean A. Irvine, May 07 2023

Example

Sequence really begins 1, 0, 0, 1, 0, 0, 2, 0, 0, 6, 0, 0, 21, 0, 0, 83, 0, 0, 356, ... but only nonzero trisection is shown.

Crossrefs

Cf. A005750, A058870, A058866, A054581.

Sequence in context: A148495 A150221 A058866 * A178325 A087649 A328435

Adjacent sequences: A063686 A063687 A063688 * A063690 A063691 A063692

Keyword

nonn

Author

Vladeta Jovovic, Aug 22 2001

Extensions

More terms from Sean A. Irvine, May 07 2023

Status

approved