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 A289195 a(n) is the number of odd integers divisible by 5 in ]4*(n-1)^2, 4*n^2[. 2
 0, 0, 2, 2, 2, 4, 4, 6, 6, 6, 8, 8, 10, 10, 10, 12, 12, 14, 14, 14, 16, 16, 18, 18, 18, 20, 20, 22, 22, 22, 24, 24, 26, 26, 26, 28, 28, 30, 30, 30, 32, 32, 34, 34, 34, 36, 36, 38, 38, 38, 40, 40, 42, 42, 42, 44, 44, 46, 46, 46, 48, 48, 50, 50, 50, 52, 52, 54 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 COMMENTS This sequence has the form (0+4k,0+4k,2+4k,2+4k,2+4k) for k>=0. LINKS Colin Barker, Table of n, a(n) for n = 0..1000 Index entries for linear recurrences with constant coefficients, signature (1,0,0,0,1,-1). FORMULA a(n + 5*k) = a(n) + 4*k. From Colin Barker, Jul 04 2017: (Start) G.f.: 2*x^2*(1 + x)*(1 - x + x^2) / ((1 - x)^2*(1 + x + x^2 + x^3 + x^4)). a(n) = a(n-1) + a(n-5) - a(n-6) for n>5. (End) MATHEMATICA Table[Count[Mod[Table[2(2(n-1)^2+k)-1, {k, 1, 4 n-2}], 5], 0], {n, 0, 50}] PROG (PARI) concat(vector(2), Vec(2*x^2*(1 + x)*(1 - x + x^2) / ((1 - x)^2*(1 + x + x^2 + x^3 + x^4)) + O(x^100))) \\ Colin Barker, Jul 04 2017 CROSSREFS Cf. A289199, A289139, A289120, A289133, A289122, A288156, A004523. Sequence in context: A246452 A104295 A172068 * A008331 A173388 A097196 Adjacent sequences:  A289192 A289193 A289194 * A289196 A289197 A289198 KEYWORD nonn,easy AUTHOR Ralf Steiner, Jun 28 2017 STATUS approved

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Last modified March 20 07:27 EDT 2019. Contains 321345 sequences. (Running on oeis4.)