A368569 - OEIS

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A368569

Irregular triangle read by rows: T(n,k) is the number of essential graphs with n nodes and k (directed or undirected) edges (n >= 1, 0 <= k <= n*(n-1)/2).

1, 1, 1, 1, 3, 6, 1, 1, 6, 27, 60, 66, 24, 1, 1, 10, 75, 350, 1120, 2130, 2595, 1730, 690, 80, 1, 1, 15, 165, 1235, 6930, 27882, 79825, 162315, 236490, 245150, 180936, 91560, 29890, 5190, 240, 1

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

OFFSET

1,5

LINKS

Table of n, a(n) for n=1..41.

EXAMPLE

Triangle T(n,k) (with n >= 1 and 0 <= k <= n*(n-1)/2) begins as follows:

1, 1;

1, 3, 6, 1;

1, 6, 27, 60, 66, 24, 1;

1, 10, 75, 350, 1120, 2130, 2595, 1730, 690, 80, 1;

...