A333158 - OEIS

A333158

Irregular triangle read by rows: T(n,k) is the number of k-regular graphs on n labeled nodes with loops allowed, n >= 1, 0 <= k <= n + 1.

1, 0, 1, 1, 1, 1, 1, 1, 0, 2, 0, 1, 1, 3, 8, 8, 3, 1, 1, 0, 38, 0, 38, 0, 1, 1, 15, 208, 730, 730, 208, 15, 1, 1, 0, 1348, 0, 20670, 0, 1348, 0, 1, 1, 105, 10126, 188790, 781578, 781578, 188790, 10126, 105, 1, 1, 0, 86174, 0, 37885204, 0, 37885204, 0, 86174, 0, 1

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,10

COMMENTS

A loop adds 2 to the degree of its vertex.

LINKS

Table of n, a(n) for n=1..63.

FORMULA

T(n,k) = T(n, n+1-k).

EXAMPLE

Triangle begins:

1, 0, 1;