OFFSET
1,2
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 1..1000
Index entries for linear recurrences with constant coefficients, signature (0,0,9,0,0,-8).
FORMULA
a(n) = M / gcd( M, 7 ), where M=2^n-1.
Conjectures from Colin Barker, Aug 23 2014, verified by Robert Israel, Nov 20 2016: (Start)
a(n) = 9*a(n-3)-8*a(n-6).
G.f.: x*(4*x^4+6*x^3+x^2+3*x+1) / ( (x-1)*(2*x-1)*(x^2+x+1)*(4*x^2+2*x+1) ). (End)
MAPLE
MATHEMATICA
Table[(2^n - 1)/GCD[2^n - 1, 7], {n, 60}] (* Vincenzo Librandi, Mar 16 2013 *)
PROG
(Magma) [(2^n - 1) / GCD (2^n - 1, 7): n in [1..40]]; // Vincenzo Librandi, Mar 16 2013
(PARI) a(n)=(2^n-1)/gcd(2^n-1, 7) \\ Edward Jiang, Sep 04 2014
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Joerg Arndt, Jun 07 2012
STATUS
approved