OFFSET
1,2
COMMENTS
Numbers n such that the determinant of the character table of the cyclic group C_n is an integer (for every n this determinant has degree at most 2 over the rationals Q). - Ahmed Fares (ahmedfares(AT)my-deja.com), Jul 16 2001
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 1..3000
Index entries for linear recurrences with constant coefficients, signature (1,0,1,-1).
FORMULA
G.f.: x*(1+x+4*x^2+2*x^3)/((1+x+x^2)*(x-1)^2). - R. J. Mathar, Dec 05 2011
a(n) = a(n-1) + a(n-3) - a(n-4) for n>4, with a(1)=1, a(2)=2, a(3)=6, a(4)=9. - Harvey P. Dale, Sep 30 2012
From Wesley Ivan Hurt, Jun 09 2016: (Start)
a(n) = (24*n-21+3*cos(2*n*Pi/3)+5*sqrt(3)*sin(2*n*Pi/3))/9.
a(3k) = 8k-2, a(3k-1) = 8k-6, a(3k-2) = 8k-7. (End)
MAPLE
A047396:=n->(24*n-21+3*cos(2*n*Pi/3)+5*sqrt(3)*sin(2*n*Pi/3))/9: seq(A047396(n), n=1..100); # Wesley Ivan Hurt, Jun 09 2016
MATHEMATICA
Flatten[#+{1, 2, 6}&/@(8*Range[0, 20])] (* or *) LinearRecurrence[ {1, 0, 1, -1}, {1, 2, 6, 9}, 80] (* Harvey P. Dale, Sep 30 2012 *)
PROG
(Magma) [n : n in [0..150] | n mod 8 in [1, 2, 6]]; // Wesley Ivan Hurt, Jun 09 2016
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
STATUS
approved