A071355 a(n) = 2*n^2 + 11*n + 12.

3, 12, 25, 42, 63, 88, 117, 150, 187, 228, 273, 322, 375, 432, 493, 558, 627, 700, 777, 858, 943, 1032, 1125, 1222, 1323, 1428, 1537, 1650, 1767, 1888, 2013, 2142, 2275, 2412, 2553, 2698, 2847, 3000, 3157, 3318, 3483, 3652, 3825, 4002, 4183, 4368, 4557, 4750, 4947

Offset

-1,1

Comments

If Y is a 3-subset of an 2n-set X then, for n>=3, a(n-3) is the number of (2 n-2)-subsets of X having at least two elements in common with Y. - Milan Janjic, Dec 16 2007

Links

G. C. Greubel, Table of n, a(n) for n = -1..5000

Index entries for linear recurrences with constant coefficients, signature (3,-3,1).

Formula

a(n) = A100345(n+4, n-1) for n>0.

a(n) = (n+4)*(2*n+3). - Reinhard Zumkeller, Nov 18 2004

From G. C. Greubel, Jul 16 2017: (Start)

a(n) = 3*a(n-1) - 3*a(n-1) + a(n-2).

G.f.: (2*x^2 - 3*x -3)/(x*(x-1)^3).

E.g.f.: (2*x^2 + 13*x + 12)*exp(x). (End)

Maple

A071355:=n->2*n^2 + 11*n + 12: seq(A071355(n), n=-1..100); # Wesley Ivan Hurt, Jul 16 2017

Mathematica

Table[2 n^2 + 11 n + 12, {n, -1, 50}] (* G. C. Greubel, Jul 16 2017 *)

Prog

(PARI) a(n)=2*n^2+11*n+12 \\ Charles R Greathouse IV, Sep 24 2015

Crossrefs

Cf. A100345.

Sequence in context: A009776 A331241 A068967 * A366984 A237650 A199242

Adjacent sequences: A071352 A071353 A071354 * A071356 A071357 A071358

Keyword

nonn,easy

Author

N. J. A. Sloane, Jun 12 2002

Status

approved