|
Search: id:A002718
|
|
|
| A002718 |
|
Number of bicoverings of an n-set.
(Formerly M4559 N1941)
|
|
+0
34
|
|
| 1, 8, 80, 1088, 19232, 424400, 11361786, 361058000, 13386003873, 570886397340, 27681861184474, 1511143062540976, 92091641176725504, 6219762391554815200, 462595509951068027741, 37676170944802047077248
(list; graph; listen)
|
|
|
OFFSET
|
2,2
|
|
|
REFERENCES
|
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).
L. Comtet, Birecouvrements et birevetements d'un ensemble fini. Studia Sci. Math. Hungar. 3 1968 137-152.
L. Comtet, Advanced Combinatorics, Reidel, 1974, p. 303, #40.
I. P. Goulden and D. M. Jackson, Combinatorial Enumeration, John Wiley and Sons, N.Y., 1983.
|
|
FORMULA
|
E.g.f. for k-block bicoverings of an n-set is exp(-x-1/2*x^2*(exp(y)-1))*Sum_{i=0..inf} x^i/i!*exp(binomial(i, 2)*y).
|
|
CROSSREFS
|
Cf. A020554, A002719, A003462, A059945-A059951. Row sums of A059443.
Sequence in context: A051580 A060375 A097815 this_sequence A057707 A145606 A002072
Adjacent sequences: A002715 A002716 A002717 this_sequence A002719 A002720 A002721
|
|
KEYWORD
|
nonn,nice,easy
|
|
AUTHOR
|
N. J. A. Sloane (njas(AT)research.att.com).
|
|
EXTENSIONS
|
More terms from Vladeta Jovovic (vladeta(AT)eunet.rs), Feb 18 2001
|
|
|
Search completed in 0.002 seconds
|
