

A289133


a(n) is the number of odd integers divisible by 9 in ]2*(n1)^2, 2*n^2[.


5



0, 0, 0, 1, 1, 1, 1, 1, 2, 2, 2, 2, 3, 3, 3, 3, 3, 4, 4, 4, 4, 5, 5, 5, 5, 5, 6, 6, 6, 6, 7, 7, 7, 7, 7, 8, 8, 8, 8, 9, 9, 9, 9, 9, 10, 10, 10, 10, 11, 11, 11, 11, 11, 12, 12, 12, 12, 13, 13, 13, 13, 13, 14, 14, 14, 14, 15, 15, 15, 15, 15, 16, 16, 16, 16, 17, 17, 17, 17, 17, 18
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OFFSET

0,9


COMMENTS

This sequence has the form (0+2k,0+2k,0+2k,1+2k,1+2k,1+2k,1+2k,1+2k,2+2k) for k>=0.


LINKS

Table of n, a(n) for n=0..80.
Index entries for linear recurrences with constant coefficients, signature (1,0,0,0,0,0,0,0,1,1).


FORMULA

a(n + 9*k) = a(n) + 2*k.
G.f.: (x^8+x^3)/(x^10x^9x+1).  Alois P. Heinz, Jun 26 2017


MATHEMATICA

Table[Count[Mod[Table[2((n1)^2 +k)1, {k, 1, 2 n1}], 9], 0], {n, 0, 50}]


PROG

(PARI) a(n) = sum(k=2*(n1)^2, 2*n^2, ((k % 2) && ((k % 9) == 0))); \\ Michel Marcus, Jun 26 2017


CROSSREFS

Cf. A289120, A289122, A288156, A004523, A289139.
Sequence in context: A097882 A108955 A108956 * A135297 A176146 A171481
Adjacent sequences: A289130 A289131 A289132 * A289134 A289135 A289136


KEYWORD

nonn,easy


AUTHOR

Ralf Steiner, Jun 25 2017


EXTENSIONS

More terms from Michel Marcus, Jun 26 2017


STATUS

approved



