A331767 Number of interior vertices formed by drawing the lines connecting any two of the 2*(n+2) perimeter points of a 3 X (n+1) square grid.

7, 29, 89, 201, 387, 641, 1067, 1599, 2305, 3233, 4431, 5855, 7721, 9853, 12369, 15477, 19093, 23141, 28073, 33557, 39699, 46773, 54815, 63681, 73825, 84833, 97005, 110579, 125587, 141733, 160063, 179913, 201105, 224409, 249329, 276215, 305925, 337345, 370793

Offset: 1

Author

Scott R. Shannon and N. J. A. Sloane, Feb 05 2020

Keywords

• nonn

Comments

Same as A331763, but only count interior crossings.

See A331452 for other illustrations.

Links

• Lars Blomberg, Table of n, a(n) for n = 1..100
• Scott R. Shannon, Colored illustration for a(3) = 89.

Crossrefs

Cf. A331763, A331765, A331766.

Extensions

Needs to be extended using the new data for A331763. - N. J. A. Sloane, Mar 12 2020

a(10) and beyond from Lars Blomberg, Apr 28 2020