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A116950 Number of functional patterns on n elements; or digraphs with maximum outdegree 1, n arrows and every point connected to an arrow. 4
1, 2, 7, 20, 61, 174, 514, 1478, 4303, 12437, 36084, 104494, 303167, 879283, 2552803, 7413583, 21544347, 62635823, 182199853, 530228946, 1543761513, 4496523995, 13102414665, 38193626823, 111375529695, 324891970936, 948051861938, 2767336312386, 8080206646244 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

COMMENTS

A001372 counts functional patterns from a set with n elements to itself; A000041 (partition function) counts functional patterns from a set with n elements to a disjoint set; this is the general case where the range may overlap the domain but may also include other values.

LINKS

Alois P. Heinz, Table of n, a(n) for n = 0..750

FORMULA

Euler transform of A002861(n) + A000081(n+1).

a(n) ~ c * d^n / sqrt(n), where d = A051491 = 2.95576528565199497471481752412..., c = 3.435908969217935496995961718... . - Vaclav Kotesovec, Sep 10 2014

EXAMPLE

For n=2 there are the following 7 digraphs:

o-+.o-+ o->o-+ o->o o-+.o->o o->o->o o->o o->o

^.|.^.| ...^.| ^..| ^.|..... ....... ...^ ....

+-+.+-+ ...+-+ +--+ +-+..... ....... o--+ o->o

CROSSREFS

Cf. A000041, A001372, A002861, A000081.

Sequence in context: A026153 A025180 A201967 * A111017 A116408 A015518

Adjacent sequences:  A116947 A116948 A116949 * A116951 A116952 A116953

KEYWORD

easy,nice,nonn

AUTHOR

Franklin T. Adams-Watters, Mar 29 2006

STATUS

approved

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Last modified November 25 18:32 EST 2014. Contains 250000 sequences.