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A055973 Number of unlabeled digraphs with loops (relations) on n nodes and with an even number of arcs. 0
1, 6, 52, 1540, 145984, 48467296, 56141454464, 229148555640864, 3333310786076963968, 174695272746896566439424, 33301710992539090379269318144, 23278728241293494584257987458067456 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Also relations considered equivalent when isomorphic and when complemented. - Christian G. Bower, Jan 05 2004

LINKS

Table of n, a(n) for n=1..12.

FORMULA

a(n)=(A000595(n)+A047832(n))/2.

a(n) = sum {1*s_1+2*s_2+...=n, 1*t_1+2*t_2=2} (fix A[s_1, s_2, ...;t_1, t_2]/(1^s_1*s_1!*2^s_2*s_2!*...*1^t_1*t_1!*2^t_2*t_2!)) where fix A[...] = prod {i, j>=1} ( (sum {d|lcm(i, j)} (d*t_d))^(gcd(i, j)*s_i*s_j)) - Christian G. Bower, Jan 05 2004

CROSSREFS

Cf. A007869, A054928.

Sequence in context: A166889 A164894 A027835 * A223345 A066357 A276365

Adjacent sequences:  A055970 A055971 A055972 * A055974 A055975 A055976

KEYWORD

easy,nonn

AUTHOR

Vladeta Jovovic, Jul 19 2000

STATUS

approved

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Last modified April 18 11:10 EDT 2019. Contains 322209 sequences. (Running on oeis4.)