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 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 (list; graph; refs; listen; history; text; internal format)
 OFFSET 5,2 REFERENCES A. O. Munagi, Set Partitions with Successions and Separations, Int. J. Math and Math. Sc. 2005, no. 3 (2005), 451-463. LINKS A. O. Munagi, Set Partitions with Successions and Separations,IJMMS 2005:3 (2005),451-463. FORMULA a(n) = binomial(n-1, 4)Bell(n-5), the case r = 4 in the general case of r pairs: c(n, r) = binomial(n-1, r)B(n-r-1). Let A be the upper Hessenberg matrix of order n defined by: A[i,i-1]=-1, A[i,j]=binomial(j-1,i-1), (i<=j), and A[i,j]=0 otherwise. Then, for n>=4, a(n+1)=(-1)^(n-4)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(n-1, 4)*combinat[bell](n-5), 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

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Last modified December 15 04:23 EST 2019. Contains 329991 sequences. (Running on oeis4.)