OFFSET
0,9
COMMENTS
This sequence has the form (0+2k,0+2k,0+2k,1+2k,0+2k,1+2k,1+2k,1+2k,2+2k, 1+2k,2+2k) for k>=0.
LINKS
Index entries for linear recurrences with constant coefficients, signature (1,0,0,0,0,0,0,0,0,0,1,-1).
FORMULA
a(n + 11*k) = a(n) + 2*k. - David A. Corneth, Jun 25 2017
G.f.: (x^10-x^9+x^8+x^5-x^4+x^3)/(x^12-x^11-x+1). - Alois P. Heinz, Jun 26 2017
MATHEMATICA
Table[Count[Mod[Table[2((n-1)^2 +k) -1, {k, 1, 2n-1}], 11], 0], {n, 0, 50}]
LinearRecurrence[{1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, -1}, {0, 0, 0, 1, 0, 1, 1, 1, 2, 1, 2, 2}, 90] (* Harvey P. Dale, Aug 24 2017 *)
PROG
(PARI) a(n) = sum(k=2*(n-1)^2, 2*n^2, ((k % 2) && ((k % 11) == 0))); \\ Michel Marcus, Jun 26 2017
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Ralf Steiner, Jun 25 2017
STATUS
approved