A339072 Triangle read by rows: T(n,k) is the number of unlabeled simple 3-connected graphs with n nodes and k edges (n >= 4, ceiling(3*n/2) <= k <= n*(n-1)/2).

1, 1, 1, 1, 2, 3, 4, 4, 2, 1, 1, 3, 14, 25, 31, 28, 17, 9, 5, 2, 1, 1, 4, 24, 101, 254, 413, 475, 426, 306, 187, 103, 52, 23, 11, 5, 2, 1, 1, 19, 204, 1068, 3348, 7152, 11199, 13683, 13604, 11374, 8203, 5216, 2963, 1536, 737, 333, 144, 62, 25, 11, 5, 2, 1, 1

Offset: 4

Author

Andrew Howroyd, Nov 24 2020

Keywords

• nonn
• tabf

Examples

			Triangle begins:
===========================================================
n/k | 6  7  8   9  10 11  12  13  14  15  16 17 18 19 20 21
----+------------------------------------------------------
  4 | 1;
  5 |       1,  1,  1;
  6 |           2,  3, 4,  4,  2,  1,  1;
  7 |                  3, 14, 25, 31, 28, 17, 9, 5, 2, 1, 1;
  8 |                      4, 24 ...
  ...
		

Links

• Andrew Howroyd, Table of n, a(n) for n = 4..732 (rows n=4..18, extracted from Robinson's tables)
• R. W. Robinson, Tables of 2-Connected and 3-Connected Graphs by Nodes and Edges, Table VI, pages 19-27.

Crossrefs

Row sums are A006290.

Column sums are A338511.

Cf. A054924, A123542, A339071.