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A218374

Number of simple labeled graphs on n nodes with an even number of components.

1, 0, 1, 3, 20, 240, 5224, 209832, 15956480, 2346694080, 675730946176, 383352300553728, 430056580863004160, 956441558748755089920, 4224552623552204307349504, 37106534862502586820794145792, 648740342428921612538202170408960, 22591362491840723496251402052982210560, 1567817841212459564387810603215973889703936

(list; graph; refs; listen; history; text; internal format)

OFFSET

0,4

LINKS

Alois P. Heinz, Table of n, a(n) for n = 0..50

FORMULA

E.g.f.: cosh(A(x)-1) where A(x) is the e.g.f. for A001187.

MATHEMATICA

nn=18; a=Sum[2^Binomial[n, 2]x^n/n!, {n, 0, nn}]; Range[0, nn]!CoefficientList[Series[Cosh[ Log[a]], {x, 0, nn}], x]

CROSSREFS

Cf. A218375.

Sequence in context: A195135 A201148 A248653 * A385830 A219541 A200527