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A084174 a(n) = 3*a(n-1) - a(n-2) - 3*a(n-3) + 2*a(n-4). 5
1, 1, 3, 6, 14, 29, 61, 124, 252, 507, 1019, 2042, 4090, 8185, 16377, 32760, 65528, 131063, 262135, 524278, 1048566, 2097141, 4194293, 8388596, 16777204, 33554419, 67108851, 134217714, 268435442, 536870897, 1073741809, 2147483632 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

COMMENTS

Original name was: Generalized Jacobsthal numbers.

Row sums of triangle A131087. - Gary W. Adamson, Jun 14 2007

LINKS

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

Index entries for linear recurrences with constant coefficients, signature (3,-1,-3,2).

FORMULA

a(n) = 2^n + (-1)^n/4 - (2*n+1)/4.

a(n+2) = a(n+1) + 2*a(n) + n, a(0)=1, a(1)=1.

a(n) = A084172(n) - A001045(n).

a(n) = floor(2^n - n*(n+1)/2). - Zerinvary Lajos, Apr 29 2007

G.f.: (1 - 2*x + x^2 + x^3)/(1 - 3*x + x^2 + 3*x^3 - 2*x^4). - Colin Barker, Jan 16 2012

MAPLE

seq(floor(2^n-n(n+1)/2), n=0..31); # Zerinvary Lajos, Apr 29 2007

MATHEMATICA

LinearRecurrence[{3, -1, -3, 2}, {1, 1, 3, 6}, 40] (* Harvey P. Dale, Feb 17 2021 *)

PROG

(MAGMA) [2^n+(-1)^n/4-(2*n+1)/4: n in [0..35]]; // Vincenzo Librandi, Jul 05 2011

CROSSREFS

Cf. A131087.

Sequence in context: A038359 A038360 A216714 * A036658 A307457 A077067

Adjacent sequences:  A084171 A084172 A084173 * A084175 A084176 A084177

KEYWORD

nonn,easy

AUTHOR

Paul Barry, May 18 2003

STATUS

approved

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Last modified May 7 15:48 EDT 2021. Contains 343651 sequences. (Running on oeis4.)