A138278 Sequence identical to its third differences in absolute values.

1, 2, 4, 8, 16, 24, 40, 80, 120, 200, 400, 600, 1000, 2000, 3000, 5000, 10000, 15000, 25000, 50000, 75000, 125000, 250000, 375000, 625000, 1250000, 1875000, 3125000, 6250000, 9375000, 15625000, 31250000, 46875000, 78125000, 156250000, 234375000, 390625000

Offset

0,2

Links

Table of n, a(n) for n=0..36.

Index entries for linear recurrences with constant coefficients, signature (0,0,5).

Formula

From R. J. Mathar, Mar 23 2010: (Start)

a(n) = 5*a(n-3), n>5.

G.f.: (3*x^3+6*x^4+4*x^5+1+2*x+4*x^2)/(1-5*x^3). (End)

Sum_{n>=0} 1/a(n) = 391/192. - Amiram Eldar, Jan 14 2024

Mathematica

Join[{1, 2, 4}, LinearRecurrence[{0, 0, 5}, {8, 16, 24}, 40]] (* Harvey P. Dale, Dec 08 2011 *)

Crossrefs

Cf. A131292, A131665, A132158, A132418, A132658.

Sequence in context: A031923 A304076 A225549 * A326078 A089827 A369151

Adjacent sequences: A138275 A138276 A138277 * A138279 A138280 A138281

Keyword

nonn,easy

Author

Paul Curtz, May 06 2008

Extensions

Edited by Charles R Greathouse IV, Mar 18 2010

More terms from Harvey P. Dale, Dec 08 2011

Status

approved