OFFSET
1,2
COMMENTS
A brain teaser.
LINKS
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) = a(n-1)+a(n-2)-a(n-3). - Wesley Ivan Hurt, Mar 14 2015
MAPLE
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
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