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A055799 T(2n+6,n), array T as in A055794. 2
1, 8, 37, 130, 385, 1012, 2431, 5434, 11440, 22880, 43758, 80444, 142766, 245480, 410210, 667964, 1062347, 1653608, 2523675, 3782350, 5574855, 8090940, 11575785, 16342950, 22789650, 31414656, 42839148, 57830872 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

COMMENTS

If Y is a 2-subset of an n-set X then, for n>=9, a(n-9) is the number of 9-subsets of X which have no exactly one element in common with Y. - Milan Janjic, Dec 28 2007

LINKS

Vincenzo Librandi, Table of n, a(n) for n = 0..1000

Index to sequences with linear recurrences with constant coefficients, signature (10,-45,120,-210,252,-210,120,-45,10,-1).

FORMULA

a(n-9)=binomial(n,9)-2*binomial(n-2,8), n=9,10,.... - Milan Janjic, Dec 28 2007

G.f.: (1-2*x+2*x^2)/(1-x)^10. [Colin Barker, Feb 21 2012]

a(n) = 10*a(n-1) - 45*a(n-2) + 120*a(n-3) - 210*a(n-4)+ 252*a(n-5) - 210*a(n-6) + 120*a(n-7) - 45*a(n-8) + 10*a(n-9) - a(n-10). Vincenzo Librandi, May 01 2012

MATHEMATICA

a=1; b=2; c=3; d=4; e=5; f=6; g=7; s=8; lst={1, s}; Do[a+=n; b+=a; c+=b; d+=c; e+=d; f+=e; g+=f; s+=g; AppendTo[lst, s], {n, 6!}]; lst [From Vladimir Joseph Stephan Orlovsky, May 24 2009]

CoefficientList[Series[(1-2*x+2*x^2)/(1-x)^10, {x, 0, 30}], x] (* Vincenzo Librandi, May 01 2012 *)

PROG

(MAGMA) [Binomial(n, 9)-2*Binomial(n-2, 8):n in [9..40]]; // Vincenzo Librandi, May 01 2012

CROSSREFS

Cf. A051601.

Sequence in context: A052387 A001780 A053296 * A035038 A240188 A111645

Adjacent sequences:  A055796 A055797 A055798 * A055800 A055801 A055802

KEYWORD

nonn,easy

AUTHOR

Clark Kimberling, May 28 2000

STATUS

approved

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Last modified November 27 23:10 EST 2014. Contains 250286 sequences.