A163383 a(n) = (n-1)*2^n - 1.

-1, 3, 15, 47, 127, 319, 767, 1791, 4095, 9215, 20479, 45055, 98303, 212991, 458751, 983039, 2097151, 4456447, 9437183, 19922943, 41943039, 88080383, 184549375, 385875967, 805306367, 1677721599, 3489660927, 7247757311, 15032385535

Offset

1,2

Comments

Prime for n = 2, 4, 5, 11, 28, 35, no more < 100.

Links

G. C. Greubel, Table of n, a(n) for n = 1..1000

Index entries for linear recurrences with constant coefficients, signature (5, -8, 4).

Formula

a(n) = A000337(n) - 2.

From R. J. Mathar, Jul 26 2009: (Start)

a(n) = 5*a(n-1) - 8*a(n-2) + 4*a(n-3).

G.f.: x*(1-8*x+8*x^2)/((x-1)*(-1+2*x)^2). (End)

Example

a(28) = ((2^(28))*(28 - 1)) - 1 = 7247757311.

Mathematica

LinearRecurrence[{5, -8, 4}, {-1, 3, 15}, 100] (* G. C. Greubel, Dec 20 2016 *)

Prog

(PARI) Vec(x*(1-8*x+8*x^2)/((x-1)*(-1+2*x)^2) + O(x^50)) \\ G. C. Greubel, Dec 20 2016

Crossrefs

Cf. A000337.

Sequence in context: A088108 A226030 A232077 * A296799 A328111 A135622

Adjacent sequences: A163380 A163381 A163382 * A163384 A163385 A163386

Keyword

easy,sign

Author

Jonathan Vos Post, Jul 25 2009

Status

approved