A307155 Number of connected, loopless 2-regular digraphs, no multiedges, on n nodes.

1, 0, 0, 1, 2, 5, 22, 90, 616, 4988, 46883, 493406, 5712809, 71909602

Offset

0,5

Comments

Inverse Euler transform of A219889.

The Multiset Transform (number of loopless 2-regular digraphs on n nodes with c weakly connected components) of this sequence starts

in row 3 as:

1 ;

2 ;

5 ;

22 , 1 ;

90 , 2 ;

616 , 8 ;

4988 , 32 , 1 ;

46883 , 149 , 2 ;

493406 , 906 , 8 ;

5712809 , 6923 , 36 , 1 ;

71909602 , 61919 , 164 , 2 ;

Links

Table of n, a(n) for n=0..13.

Crossrefs

Cf. A219889 (not necessarily connected), A005642 (loops admitted).

Sequence in context: A083465 A339646 A215100 * A144934 A346628 A371609

Adjacent sequences: A307152 A307153 A307154 * A307156 A307157 A307158

Keyword

nonn

Author

R. J. Mathar, Mar 27 2019

Status

approved