A096406 a(1) = 4; then alternately add -4 and multiply by -2.

4, 0, 0, -4, 8, 4, -8, -12, 24, 20, -40, -44, 88, 84, -168, -172, 344, 340, -680, -684, 1368, 1364, -2728, -2732, 5464, 5460, -10920, -10924, 21848, 21844, -43688, -43692, 87384, 87380, -174760, -174764, 349528, 349524, -699048, -699052, 1398104, 1398100, -2796200, -2796204, 5592408, 5592404

Offset

1,1

Comments

Applet randomly selects from among nine algorithms and each algorithm has its own random parameters. Six terms are presented and you get to guess the next term.

Links

Table of n, a(n) for n=1..46.

Alexander Bogomolny's Cut-the-Knot.org, What's Next?

Index entries for linear recurrences with constant coefficients, signature (0,-1,0,2).

Formula

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

a(n) = (1/3)*(2 - 6(-1)^n - 2(-2)^ceiling(n/2)). - Ralf Stephan, Dec 04 2004

O.g.f.: 4*x*(-1 - x^2 + x^3)/((-1+x)*(1+x)*(1+2*x^2)). - R. J. Mathar, Dec 05 2007

a(n) = -a(n-2) + 2*a(n-4); a(1)=4, a(2)=0, a(3)=0, a(4)=-4. - Harvey P. Dale, May 01 2016

Mathematica

LinearRecurrence[{0, -1, 0, 2}, {4, 0, 0, -4}, 50] (* Harvey P. Dale, May 01 2016 *)

Crossrefs

Sequence in context: A096904 A308257 A308256 * A189885 A151673 A005397

Adjacent sequences: A096403 A096404 A096405 * A096407 A096408 A096409

Keyword

sign,easy

Author

Herman DeWeerd (bhdeweerd(AT)worldnet.att.net), Aug 07 2004

Extensions

Description found by Ray Chandler, Aug 07 2004

Status

approved