login

Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 61st year, we have over 378,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”).

Triangle read by rows: T(n,k) is the number of bicolored cubic graphs on 2n unlabeled vertices with k vertices of the first color, n >= 0, 0 <= k <= 2*n.
7

%I #13 Mar 11 2023 19:48:36

%S 1,0,0,0,1,1,1,1,1,2,2,5,5,5,2,2,6,11,33,48,66,48,33,11,6,21,68,257,

%T 556,950,1071,950,556,257,68,21,94,510,2443,7126,15393,23644,27606,

%U 23644,15393,7126,2443,510,94,540,4712,27682,102122,270957,526783,781292,887305,781292,526783,270957,102122,27682,4712,540

%N Triangle read by rows: T(n,k) is the number of bicolored cubic graphs on 2n unlabeled vertices with k vertices of the first color, n >= 0, 0 <= k <= 2*n.

%C Adjacent vertices may have the same color.

%H Andrew Howroyd, <a href="/A361361/b361361.txt">Table of n, a(n) for n = 0..440</a> (rows 0..20)

%e Triangle begins:

%e 1

%e 0, 0, 0;

%e 1, 1, 1, 1, 1;

%e 2, 2, 5, 5, 5, 2, 2;

%e 6, 11, 33, 48, 66, 48, 33, 11, 6;

%e 21, 68, 257, 556, 950, 1071, 950, 556, 257, 68, 21;

%e ...

%Y Columns k=0..2 are A005638, A361410, A361411.

%Y Row sums are A361362.

%Y Central coefficients are A361409.

%Y Cf. A321304 (connected), A361404.

%K nonn,tabf

%O 0,10

%A _Andrew Howroyd_, Mar 10 2023