A060379 Number of self-avoiding polygons on the 2-dimensional square lattice with perimeter 2n with at most 4 horizontal edges in each vertical cross-section.
1, 2, 7, 28, 124, 588, 2938, 15266, 81770, 448698, 2510813, 14277838, 82286365, 479610362, 2822332127, 16745262798
Offset: 2
Examples
a(3) = 2 because there are 2 self-avoiding polygons of perimeter 2*3 with at most 4 horizontal edges per vertical cross-section.
Links
- Doron Zeilberger, The Umbral Transfer-Matrix Method. IV. Counting Self-AvoidingPolygons and walks; Local copy [Pdf file only, no active links]
Formula
See Appendix 2 of the reference (a 7-page system of linear functional equations for 5 unknown generating functions, one of which is the desired generating function).