OFFSET
1,3
COMMENTS
Nonnegative k such that k or 6*k + 1 is divisible by 7. - Bruno Berselli, Feb 13 2018
LINKS
David Lovler, Table of n, a(n) for n = 1..1000
Index entries for linear recurrences with constant coefficients, signature (1,1,-1).
FORMULA
a(n) = 7*n - a(n-1) - 13 for n>1, a(1)=0. - Vincenzo Librandi, Aug 05 2010
From R. J. Mathar, Oct 08 2011: (Start)
a(n) = 7*n/2 - 19/4 - 5*(-1)^n/4.
G.f.: x^2*(1 + 6*x) / ((1 + x)*(x - 1)^2). (End)
E.g.f.: 6 + ((14*x - 19)*exp(x) - 5*exp(-x))/4. - David Lovler, Aug 31 2022
PROG
(PARI) forstep(n=0, 200, [1, 6], print1(n", ")) \\ Charles R Greathouse IV, Oct 17 2011
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
STATUS
approved