A289139 a(n) is the number of odd integers divisible by 7 in ]4*(n-1)^2, 4*n^2[.

0, 0, 1, 2, 2, 2, 3, 4, 4, 5, 6, 6, 6, 7, 8, 8, 9, 10, 10, 10, 11, 12, 12, 13, 14, 14, 14, 15, 16, 16, 17, 18, 18, 18, 19, 20, 20, 21, 22, 22, 22, 23, 24, 24, 25, 26, 26, 26, 27, 28, 28, 29, 30, 30, 30, 31, 32, 32, 33, 34, 34, 34, 35, 36, 36, 37, 38, 38, 38, 39, 40, 40

Offset

0,4

Comments

This sequence has the form (0+4k,0+4k,1+4k,2+4k,2+4k,2+4k,3+4k) for k>=0.

Links

Table of n, a(n) for n=0..71.

Index entries for linear recurrences with constant coefficients, signature (1,0,0,0,0,0,1,-1).

Formula

a(n + 7*k) = a(n) + 4*k.

G.f.: (x^7+x^6+x^3+x^2)/(x^8-x^7-x+1). - Alois P. Heinz, Jun 26 2017

Mathematica

Table[Count[Mod[Table[2(2(n-1)^2 +k)-1, {k, 1, 4 n-2}], 7], 0], {n, 0, 100}]

Crossrefs

Cf. A289120, A289133, A289122, A288156, A004523.

Sequence in context: A358901 A070547 A319922 * A094838 A025768 A000929

Adjacent sequences: A289136 A289137 A289138 * A289140 A289141 A289142

Keyword

nonn,easy

Author

Ralf Steiner, Jun 26 2017

Status

approved