|
Search: id:A005784
|
|
|
| A005784 |
|
Number of 4-covers of an n-set.
(Formerly M3535)
|
|
+0
4
|
|
| 4, 17, 65, 230, 736, 2197, 6093, 15864, 38960, 90837, 202005, 430577, 883057, 1748909, 3355213, 6252575, 11345602, 20089514, 34778306, 58964020, 98053576, 160151566, 257229974, 406739271, 633795181, 974126408, 1477999320
(list; graph; listen)
|
|
|
OFFSET
|
1,1
|
|
|
REFERENCES
|
R. J. Clarke, Covering a set by subsets, Discrete Math., 81 (1990), 147-152.
|
|
LINKS
|
Vladeta Jovovic, Binary matrices up to row and column permutations
|
|
FORMULA
|
G.f.: (x^20 - x^19 + 4*x^18 + 9*x^17 + 23*x^16 + 39*x^15 + 90*x^14 + 131*x^13 + 204*x^12 + 238*x^11 + 252*x^10 + 238*x^9 + 204*x^8 + 131*x^7 + 90*x^6 + 39*x^5 + 23*x^4 + 9*x^3 + 4*x^2 - x + 1)/((1 - x^4)^3*(1 - x^3)^4*(1 - x^2)^3*(1 - x)^5).
|
|
CROSSREFS
|
Cf. A006148, A005783, A005785.
Sequence in context: A006762 A122231 A119916 this_sequence A095252 A102207 A045992
Adjacent sequences: A005781 A005782 A005783 this_sequence A005785 A005786 A005787
|
|
KEYWORD
|
easy,nonn
|
|
AUTHOR
|
njas
|
|
EXTENSIONS
|
More terms from Vladeta Jovovic (vladeta(AT)Eunet.yu), Jun 03 2000
|
|
|
Search completed in 0.002 seconds
|
