

A105481


Number of partitions of {1...n} containing 4 pairs of consecutive integers, where each pair is counted within a block and a string of more than 2 consecutive integers are counted two at a time.


5



1, 5, 30, 175, 1050, 6552, 42630, 289410, 2049300, 15120105, 116090975, 926248050, 7668746540, 65793760060, 584151925320, 5360347320420, 50776288702215, 495946245776940, 4989391837053085, 51648932225779735, 549620905409062872
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OFFSET

5,2


REFERENCES

A. O. Munagi, Set Partitions with Successions and Separations, Int. J. Math and Math. Sc. 2005, no. 3 (2005), 451463.


LINKS

Table of n, a(n) for n=5..25.
A. O. Munagi, Set Partitions with Successions and Separations,IJMMS 2005:3 (2005),451463.


FORMULA

a(n) = binomial(n1, 4)Bell(n5), the case r = 4 in the general case of r pairs: c(n, r) = binomial(n1, r)B(nr1).
Let A be the upper Hessenberg matrix of order n defined by: A[i,i1]=1, A[i,j]=binomial(j1,i1), (i<=j), and A[i,j]=0 otherwise. Then, for n>=4, a(n+1)=(1)^(n4)coeff(charpoly(A,x),x^4). [From Milan Janjic, Jul 08 2010]


EXAMPLE

a(6) = 5 because the partitions of {1,2,3,4,5,6} with 4 pairs of consecutive integers are 12345/6,1234/56,123/456,12/3456,1/23456.


MAPLE

seq(binomial(n1, 4)*combinat[bell](n5), n=5..25);


CROSSREFS

Cf. A105480, A105482, A105486, A105491, A105494.
Sequence in context: A276598 A057088 A156195 * A242157 A094167 A051738
Adjacent sequences: A105478 A105479 A105480 * A105482 A105483 A105484


KEYWORD

easy,nonn


AUTHOR

Augustine O. Munagi, Apr 10 2005


STATUS

approved



