OFFSET
1,1
FORMULA
a(n) = 14*n - a(n-1) - 14 (with a(1) = 3). - Vincenzo Librandi, Nov 13 2010
From Wolfdieter Lang, Dec 15 2011: (Start)
a(n) = 7*n-(7-(-1)^n)/2.
O.g.f.: x*(3+8*x+3*x^2)/((1+x)*(1-x)^2).
See the Bruno Berselli contribution under A113801. (End)
Sum_{n>=1} (-1)^(n+1)/a(n) = cot(3*Pi/14)*Pi/14. - Amiram Eldar, Dec 30 2021
MATHEMATICA
{3+#, 11+#}&/@(14*Range[0, 30])//Flatten (* Harvey P. Dale, Jun 28 2020 *)
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Giovanni Teofilatto, Jan 22 2006
STATUS
approved