A325447 Triangle read by rows: T(n,k) is the number of nonseparable (or 2-connected) graphs on n unlabeled nodes with circumference k, (n >= 3, k >= 3).

1, 0, 3, 0, 2, 8, 0, 2, 6, 48, 0, 2, 9, 74, 383, 0, 2, 10, 159, 756, 6196, 0, 2, 13, 276, 2058, 14634, 177083, 0, 2, 14, 505, 4824, 48137, 384942, 9305118

Offset

3,3

Links

Table of n, a(n) for n=3..38.

Eric Weisstein's World of Mathematics, Graph Circumference

Eric Weisstein's World of Mathematics, Hamiltonian Graph

Formula

T(n, 4) = 2 for n > 4.

Example

Triangle begins, (n >= 3, k >= 3):
  1;
  0, 3;
  0, 2,  8;
  0, 2,  6,  48;
  0, 2,  9,  74,  383;
  0, 2, 10, 159,  756,  6196;
  0, 2, 13, 276, 2058, 14634, 177083;
  0, 2, 14, 505, 4824, 48137, 384942, 9305118;
  ...

Crossrefs

Row sums are A002218(n >= 3).

Right diagonal is A003216.

Cf. A128042, A325455.

Sequence in context: A303410 A126671 A209437 * A240660 A347418 A330646

Adjacent sequences: A325444 A325445 A325446 * A325448 A325449 A325450

Keyword

nonn,tabl,more

Author

Andrew Howroyd, Sep 06 2019

Status

approved