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Search: id:A130221
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| A130221 |
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Number of partitions of n-set in which number of blocks of size 2k is odd (or zero) for every k. |
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+0
1
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| 1, 1, 2, 5, 12, 37, 158, 667, 2740, 13461, 74710, 412095, 2406880, 15450541, 103187698, 715323395, 5236160612, 40014337437, 318488475658, 2637143123027, 22603231117364, 201268520010153, 1855401760331982, 17624602999352535
(list; graph; listen)
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OFFSET
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0,3
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FORMULA
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E.g.f.: exp(sinh(x))*Product_{k>0} (1+sinh(x^(2*k)/(2*k)!)).
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EXAMPLE
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a(4)=12 because from the 15 (=A000110(4)) partitions of the 4-set {a,b,c,d} only the partitions ab|cd, ac|bd, and ad|bc do not qualify.
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MAPLE
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g:=exp(sinh(x))*(product(1+sinh(x^(2*k)/factorial(2*k)), k=1..25)): gser:= series(g, x=0, 30): seq(factorial(n)*coeff(gser, x, n), n=0..23); - Emeric Deutsch (deutsch(AT)duke.poly.edu), Aug 28 2007
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CROSSREFS
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Cf. A000110, A102759.
Adjacent sequences: A130218 A130219 A130220 this_sequence A130222 A130223 A130224
Sequence in context: A003724 A138314 A115277 this_sequence A036782 A050237 A050258
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KEYWORD
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easy,nonn
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AUTHOR
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Vladeta Jovovic (vladeta(AT)Eunet.yu), Aug 05 2007, Aug 05 2007
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EXTENSIONS
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More terms from Emeric Deutsch (deutsch(AT)duke.poly.edu), Aug 28 2007
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