OFFSET
0,4
EXAMPLE
a(4)=8 because there are eleven graphs with 4 nodes but three have (at least two) components that are identical: * * * * , *-* *-* , * * *-*
MATHEMATICA
nn=19; a={1, 1, 2, 6, 21, 112, 853, 11117, 261080, 11716571, 1006700565, 164059830476, 50335907869219, 29003487462848061, 31397381142761241960, 63969560113225176176277, 245871831682084026519528568, 1787331725248899088890200576580, 24636021429399867655322650759681644}; CoefficientList[Series[Product[(1+x^i)^a[[i]], {i, 1, nn}], {x, 0, nn}], x]
CROSSREFS
KEYWORD
nonn
AUTHOR
Geoffrey Critzer, Feb 20 2012
STATUS
approved