A241156 Number of complementary pairs of `homogenized' N-free graphs with n nodes.

1, 1, 2, 7, 22, 82, 308, 1225, 4954, 20558, 86572, 369942, 1598172, 6972100, 30663656, 135826627, 605386062, 2713066882, 12217967284, 55262144418, 250932354484, 1143468874748, 5227460728344, 23968152050930, 110191808568852, 507857114699628

Offset: 1

Author

N. J. A. Sloane, Apr 18 2014

Keywords

• nonn

Links

• P. J. Cameron, Some treelike objects, Quart. J. Math. Oxford, 38 (1987), 155-183. See p. 166.
• Jacinta Covington, A universal structure for N-free graphs, Proc. London Math. Soc. (3) 58 (1989), no. 1, 1--16. MR0969544 (89m:03028).

Crossrefs

Cf. A226909.

Formula

a(1)=1, thereafter a(n) = A226909(n)/2.