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A290707 a(n) = 2^(n+1) + n^2 - 1. 2
1, 4, 11, 24, 47, 88, 163, 304, 575, 1104, 2147, 4216, 8335, 16552, 32963, 65760, 131327, 262432, 524611, 1048936, 2097551, 4194744, 8389091, 16777744, 33555007, 67109488, 134218403, 268436184, 536871695, 1073742664, 2147484547, 4294968256, 8589935615 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

COMMENTS

For n > 1, also the number of irredundant sets in the complete bipartite graph K_{n,n}.

For n > 1, also the number of irredundant sets in the 2 X n rook graph. - Andrew Howroyd, Aug 11 2017

LINKS

Table of n, a(n) for n=0..32.

Eric Weisstein's World of Mathematics, Complete Bipartite Graph

Eric Weisstein's World of Mathematics, Irredundant Set

Index entries for linear recurrences with constant coefficients, signature (5,-9,7,-2).

FORMULA

a(n) = 2^(n+1) + n^2 - 1.

a(n) = 5*a(n-1) - 9*a(n-2) + 7*a(n-3) - 2*a(n-4).

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

MATHEMATICA

Table[2^(n + 1) + n^2 - 1, {n, 0, 40}]

LinearRecurrence[{5, -9, 7, -2}, {4, 11, 24, 47}, {0, 20}]

CoefficientList[Series[(1 - x - 2 x^3)/((-1 + x)^3 (-1 + 2 x)), {x, 0, 20}], x]

PROG

(PARI) a(n)=2^(n+1)+n^2-1 \\ Charles R Greathouse IV, Aug 09 2017

CROSSREFS

Cf. A290709, A290818.

Sequence in context: A160860 A192748 A143075 * A260057 A260150 A258472

Adjacent sequences:  A290704 A290705 A290706 * A290708 A290709 A290710

KEYWORD

nonn,easy

AUTHOR

Eric W. Weisstein, Aug 09 2017

STATUS

approved

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Last modified October 15 16:01 EDT 2018. Contains 316236 sequences. (Running on oeis4.)