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A122088 Add 10, subtract 5, add 10, subtract 5, ad infinitum. 1
1, 11, 6, 16, 11, 21, 16, 26, 21, 31, 26, 36, 31, 41, 36, 46, 41, 51, 46, 56, 51, 61, 56, 66, 61, 71, 66, 76, 71, 81, 76, 86, 81, 91, 86, 96, 91, 101, 96, 106, 101, 111, 106, 116, 111, 121, 116, 126, 121, 131, 126, 136, 131, 141, 136, 146, 141, 151, 146, 156, 151, 161, 156, 166, 161, 171 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

A brain teaser.

LINKS

Table of n, a(n) for n=1..66.

Math. Central U. Regina, no. 377 of QQ03

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

FORMULA

a(2j+1) = 5j+1, a(2j) = 5j+6. - Robert G. Wilson v, Nov 26 2006; R. J. Mathar, Jul 09 2009

From R. J. Mathar, Jul 09 2009: (Start)

G.f.: x*(1+10*x-6*x^2)/((1+x)*(1-x)^2).

a(n) = 9/4+5*n/2+15*(-1)^n/4. (End)

a(n+1) = (5/2)*[1+3*(-1)^n]+a(n), with a(1)=1. - Paolo P. Lava, Jul 21 2009

a(n) = a(n-1)+a(n-2)-a(n-3). - Wesley Ivan Hurt, Mar 14 2015

MAPLE

A122088:=n->9/4 + 5*n/2 + 15*(-1)^n/4: seq(A122088(n), n=1..50); # Wesley Ivan Hurt, Mar 14 2015

MATHEMATICA

Table[9/4 + 5*n/2 + 15*(-1)^n/4, {n, 50}] (* Wesley Ivan Hurt, Mar 14 2015 *)

LinearRecurrence[{1, 1, -1}, {1, 11, 6}, 70] (* Harvey P. Dale, Dec 06 2017 *)

PROG

(MAGMA) [9/4 + 5*n/2 + 15*(-1)^n/4 : n in [1..50]]; // Wesley Ivan Hurt, Mar 14 2015

CROSSREFS

Sequence in context: A080501 A122098 A115943 * A304053 A190624 A241308

Adjacent sequences:  A122085 A122086 A122087 * A122089 A122090 A122091

KEYWORD

nonn,easy

AUTHOR

Chris H. (chrishale(AT)deotte.com), Oct 17 2006

EXTENSIONS

Present definition supplied by R. J. Mathar, Oct 20 2006

More terms from Robert G. Wilson v, Nov 26 2006

Formulas adapted to offset by R. J. Mathar, Jul 09 2009

STATUS

approved

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Last modified November 11 15:51 EST 2019. Contains 329019 sequences. (Running on oeis4.)