OFFSET
3,1
LINKS
Seiichi Manyama, Table of n, a(n) for n = 3..500
P. W. Kasteleyn, The Statistics of Dimers on a Lattice, Physica, 27 (1961), 1209-1225.
FORMULA
G.f: 2*x^3*(112+882*x-8955*x^2-22184*x^3+151298*x^4+192108*x^5-1004174*x^6-773678*x^7+3077791*x^8+1598624*x^9-4646368*x^10-1738444*x^11+3589216*x^12+ 1010882*x^13-1408253*x^14-318388*x^15+271982*x^16+52648*x^17-23250*x^18-4062*x^19+601*x^20+100*x^21)/((1-x)*(1+x)*(1+5*x+x^2)*(1-5*x+x^2)*(1-2*x-x^2)* (1+2*x-x^2)*(1+x-x^2)*(1-x-x^2)*(1-5*x^2+x^4)*(1-6*x-3*x^2+6*x^3+x^4)).
CROSSREFS
KEYWORD
nonn
AUTHOR
Sergey Perepechko, Nov 30 2013
STATUS
approved