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A060823 4-wave sequence beginning with 2's with middles dropped. 1
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 (list; graph; refs; listen; history; text; internal format)
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 * A178076 A292476 A259807

Adjacent sequences:  A060820 A060821 A060822 * A060824 A060825 A060826

KEYWORD

easy,nonn

AUTHOR

Jason Earls, May 01 2001

STATUS

approved

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Last modified January 20 14:13 EST 2019. Contains 319333 sequences. (Running on oeis4.)