A379432 Triangle read by rows: T(n,k) is the number of unsensed 2-connected (nonseparable) planar maps with n edges and k vertices, n >= 2, 2 <= k <= n.

1, 1, 1, 1, 1, 1, 1, 2, 2, 1, 1, 3, 7, 3, 1, 1, 4, 13, 13, 4, 1, 1, 5, 29, 44, 29, 5, 1, 1, 7, 51, 139, 139, 51, 7, 1, 1, 8, 92, 370, 623, 370, 92, 8, 1, 1, 10, 147, 913, 2307, 2307, 913, 147, 10, 1, 1, 12, 240, 2048, 7644, 11673, 7644, 2048, 240, 12, 1, 1, 14, 357, 4295, 22344, 50174, 50174, 22344, 4295, 357, 14, 1

Offset

2,8

Comments

The maps considered here may include parallel edges.

The number of faces is n + 2 - k.

Links

Table of n, a(n) for n=2..79.

Timothy R. Walsh, Number of sensed planar maps with n edges and m vertices, pp. 29-36.

Formula

T(n,k) = T(n, n+2-k).

Example

Triangle begins:
   1;
   1,  1;
   1,  1,   1;
   1,  2,   2,   1;
   1,  3,   7,   3,    1;
   1,  4,  13,  13,    4,    1;
   1,  5,  29,  44,   29,    5,   1;
   1,  7,  51, 139,  139,   51,   7,   1;
   1,  8,  92, 370,  623,  370,  92,   8,  1;
   1, 10, 147, 913, 2307, 2307, 913, 147, 10, 1;
   ...

Crossrefs

Row sums are A006403.

Cf. A082680 (rooted), A342061 (sensed), A212438 (3-connected), A277741, A342060.

Sequence in context: A371830 A266378 A092113 * A331485 A342061 A045995

Adjacent sequences: A379429 A379430 A379431 * A379433 A379434 A379435

Keyword

nonn,tabl

Author

Andrew Howroyd, Jan 14 2025

Status

approved