OFFSET
2,1
LINKS
Andrew Howroyd, Table of n, a(n) for n = 2..500
Eric Weisstein's World of Mathematics, Graph Cycle
Eric Weisstein's World of Mathematics, Grid Graph
FORMULA
Empirical g.f.: -x^2 * (15 - 325*x + 3889*x^2 - 32204*x^3 + 166496*x^4 - 439661*x^5 + 117553*x^6 + 2506529*x^7 - 5691052*x^8 - 128310*x^9 + 16209330*x^10 - 15148184*x^11 - 17089827*x^12 + 28709449*x^13 + 11141815*x^14 - 27136640*x^15 - 13792528*x^16 + 20876587*x^17 + 15963209*x^18 - 11646759*x^19 - 10681356*x^20 + 3192142*x^21 + 3419602*x^22 - 252986*x^23 - 401310*x^24 - 43774*x^25 + 13852*x^26 + 2950*x^27 - 278*x^28 - 48*x^29 + 4*x^30) / ((-1 + x)^2 * (-1 + 38*x - 580*x^2 + 4945*x^3 - 26274*x^4 + 84913*x^5 - 122213*x^6 - 183068*x^7 + 1124479*x^8 - 1544617*x^9 - 1129508*x^10 + 5346947*x^11 - 3023145*x^12 - 6147688*x^13 + 6904233*x^14 + 3952819*x^15 - 5690282*x^16 - 4144167*x^17 + 3164355*x^18 + 4915006*x^19 - 1267655*x^20 - 3336331*x^21 + 82962*x^22 + 1051157*x^23 + 93428*x^24 - 119962*x^25 - 23089*x^26 + 2688*x^27 + 1368*x^28 - 34*x^29 - 30*x^30 + 2*x^31)). - Vaclav Kotesovec, Dec 09 2020
PROG
CROSSREFS
KEYWORD
nonn
AUTHOR
Seiichi Manyama, Nov 24 2020
EXTENSIONS
Terms a(13) and beyond from Andrew Howroyd, Dec 08 2020
STATUS
approved