A060823 4-wave sequence beginning with 2's with middles dropped.

2, 2, 8, 20, 60, 170, 492, 1414, 4074, 11728, 33772, 97240, 279994, 806208, 2321386, 6684162, 19246280, 55417452, 159568196, 459458306, 1322957468, 3809304206, 10968454314, 31582405472, 90937912212, 261845282320, 753953441490

Offset

2,1

Links

Harry J. Smith, Table of n, a(n) for n = 2..200

F. v. Lamoen, Wave sequences

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

Formula

a(n) = 2*a(n-1) + 3*a(n-2) - a(n-3) - a(n-4). - Antonio G. Astudillo (afg_astudillo(AT)lycos.com), Mar 22 2003

From R. J. Mathar, Jul 15 2009: (Start)

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

a(n) = 2*A006357(n-3). (End)

Mathematica

LinearRecurrence[{2, 3, -1, -1}, {2, 2, 8, 20}, 30] (* Harvey P. Dale, Aug 31 2016 *)

Prog

(PARI) { for (n=2, 200, if (n>5, a=2*a1 + 3*a2 - a3 - a4; a4=a3; a3=a2; a2=a1; a1=a, if (n==2, a=a4=2, if (n==3, a=a3=2, if (n==4, a=a2=8, a=a1=20)))); write("b060823.txt", n, " ", a); ) } \\ Harry J. Smith, Jul 12 2009

Crossrefs

Cf. A038197.

Sequence in context: A098277 A242658 A080040 * A330645 A178076 A292476

Adjacent sequences: A060820 A060821 A060822 * A060824 A060825 A060826

Keyword

easy,nonn

Author

Jason Earls, May 01 2001

Status

approved