OFFSET
1,1
COMMENTS
Also, numbers of the form 169k +- 70.
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 1..10000
Index entries for linear recurrences with constant coefficients, signature (1,1,-1).
FORMULA
a(n) = a(n-1) + a(n-2) - a(n-3).
G.f.: x*(70 + 29*x + 70*x^2) / ( (1+x)*(x-1)^2 ). - Alexander R. Povolotsky, Feb 15 2009
Sum_{n>=1} (-1)^(n+1)/a(n) = tan(29*Pi/338)*Pi/169. - Amiram Eldar, Feb 26 2023
MATHEMATICA
LinearRecurrence[{1, 1, -1}, {70, 99, 239}, 50]
PROG
(Magma) [Floor(n/2)*169-70*(-1)^n: n in [1..50]];
(PARI) a(n)=n\2*169-70*(-1)^n \\ Charles R Greathouse IV, Dec 23 2011
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Vincenzo Librandi, Feb 14 2009
STATUS
approved