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A210714
Number of disconnected regular simple graphs on n vertices with girth exactly 4.
1
0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 3, 2, 5, 3, 15, 5, 44, 10, 203, 47, 1415, 1710, 27771, 197951, 2613710, 33117920, 463707092, 6709514282, 102306345333, 1597440872721
OFFSET
0,13
FORMULA
a(n) = A185214(n) - A185215(n).
MATHEMATICA
A[s_Integer] := With[{s6 = StringPadLeft[ToString[s], 6, "0"]}, Cases[ Import["https://oeis.org/A" <> s6 <> "/b" <> s6 <> ".txt", "Table"], {_, _}][[All, 2]]];
A185214 = A@185214;
A185215 = A@185215;
a[n_] := A185214[[n + 1]] - A185215[[n + 1]];
a /@ Range[0, 31] (* Jean-François Alcover, Jan 27 2020 *)
CROSSREFS
Sequence in context: A331847 A130912 A178844 * A343782 A363447 A371905
KEYWORD
nonn,more,hard
AUTHOR
Jason Kimberley, Dec 10 2012
EXTENSIONS
a(31) corrected by the author, propagated from A185244, Jan 05 2013
STATUS
approved