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A005744 G.f.: x*(1+x-x^2)/((1-x)^4*(1+x)).
(Formerly M3360)
+0
9
0, 1, 4, 9, 17, 28, 43, 62, 86, 115, 150, 191, 239, 294, 357, 428, 508, 597, 696, 805, 925, 1056, 1199, 1354, 1522, 1703, 1898, 2107, 2331, 2570, 2825, 3096, 3384, 3689, 4012, 4353, 4713, 5092, 5491, 5910, 6350, 6811, 7294, 7799, 8327, 8878, 9453, 10052 (list; graph; listen)
OFFSET

0,3

COMMENT

Number of n-covers of a 2-set.

a(n)=A002623(n)-(n+1).

Boolean switching functions a(n,s) for s = 2.

REFERENCES

R. J. Clarke, Covering a set by subsets, Discrete Math., 81 (1990), 147-152.

LINKS

T. D. Noe, Table of n, a(n) for n=0..1000

Vladeta Jovovic, Binary matrices up to row and column permutations

Index entries for sequences related to Boolean functions

FORMULA

a(n) = n*(n-1)/2 + Sum((n-2*i+1)*(n-2*i)/2, i=1..floor( (n+1)/2 )). - njas, Nov 28 2003

CROSSREFS

John Layman (layman(AT)calvin.math.vt.edu) observes that A003453 appears to be the alternating sum transform (PSumSIGN) of A005744.

Cf. A002623, A005745, A005746, A005747, A005748, A005771, A003180.

Cf. A052265.

Adjacent sequences: A005741 A005742 A005743 this_sequence A005745 A005746 A005747

Sequence in context: A008023 A008055 A137441 this_sequence A027367 A009879 A009878

KEYWORD

easy,nonn,nice

AUTHOR

njas, Simon Plouffe (plouffe(AT)math.uqam.ca)

EXTENSIONS

Additional comments from Alford Arnold (Alford1940(AT)aol.com)

More terms from Vladeta Jovovic (vladeta(AT)Eunet.yu), May 25 2000

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Last modified October 12 15:26 EDT 2008. Contains 144830 sequences.


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