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

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 * A219541 A200527 A237431

Adjacent sequences: A218371 A218372 A218373 * A218375 A218376 A218377

Keyword

nonn

Author

Geoffrey Critzer, Oct 27 2012

Status

approved