%I #8 May 07 2023 23:24:53

%S 1,1,2,6,21,83,356,1599,7434,35381,171508,843419,4197179,21094355,

%T 106915928,545859112,2804656069,14491370996,75248398034,392476363133,

%U 2055245992376,10801442696736,56953957110855,301207378815752,1597342159296786,8492297139795170

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

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

%F a(n) = A058870(n) + A063687(n) with A058870(0)=0. - _Sean A. Irvine_, May 07 2023

%e 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.

%Y Cf. A005750, A058870, A058866, A054581.

%K nonn

%O 1,3

%A _Vladeta Jovovic_, Aug 22 2001

%E More terms from _Sean A. Irvine_, May 07 2023