

A097763


Number of different partitions of the set {1, 2, ..., n} into an even number of blocks such that each block contains at least 2 elements.


2



0, 0, 0, 3, 10, 25, 56, 224, 1506, 9951, 57992, 315425, 1761552, 11022180, 78474748, 603715831, 4771273414, 38070877273, 309146434240, 2598546954268, 22887194502518, 211388690471531, 2031261113410564, 20121026325645745
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OFFSET

1,4


COMMENTS

A097762(n)+A097763(n) = A000296(n).


LINKS

Table of n, a(n) for n=1..24.


FORMULA

Exponential generating function: cosh(exp(x)x1).


EXAMPLE

a(6)=25 since we can partition a set of six elements into two nonsingleton blocks, either of sizes four and two (15 ways) or three and three (10 ways); a(6)=15+10=25.


MAPLE

seq(coeff(series(cosh(exp(x)x1), x=0, 25), x^i)*i!, i=1..24);


CROSSREFS

Cf. A000296, A097762.
Sequence in context: A047667 A192963 A000247 * A034506 A067988 A005674
Adjacent sequences: A097760 A097761 A097762 * A097764 A097765 A097766


KEYWORD

easy,nonn


AUTHOR

Isabel C. Lugo (izzycat(AT)gmail.com), Aug 23 2004


STATUS

approved



