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 A210444 a(n) = |{0
 0, 0, 1, 2, 0, 4, 1, 0, 2, 2, 0, 4, 0, 1, 4, 2, 0, 6, 1, 3, 2, 2, 0, 5, 2, 1, 3, 1, 2, 11, 0, 1, 4, 1, 2, 6, 0, 2, 4, 3, 1, 9, 2, 3, 4, 2, 0, 7, 1, 4, 4, 5, 0, 8, 4, 1, 3, 3, 0, 15, 0, 3, 4, 4, 4, 13, 2, 4, 2, 5, 2, 10, 0, 2, 11, 2, 3, 12, 0, 6, 6, 2, 2, 13, 3, 5, 7, 5, 1, 16, 4, 4, 6, 3, 2, 11, 0, 8, 6, 7 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,4 COMMENTS Conjecture: a(n)>0 for all n>911. This implies that for each n=2,3,4,... there is a positive integer k0&&(n<3||Mod[n, 2]+Con[n]==0) a[n_]:=a[n]=Sum[If[PrimeQ[k*n-1]==True&&PrimeQ[k*n+1]==True&&pr[k*n]==True, 1, 0], {k, 1, n-1}] Do[Print[n, " ", a[n]], {n, 1, 100}] CROSSREFS Cf. A005153, A071558, A208243, A208244, A208246, A208249, A209236, A209253, A209254, A209312, A219185, A219312, A219315, A219320. Sequence in context: A112081 A265158 A366907 * A226949 A166589 A332696 Adjacent sequences: A210441 A210442 A210443 * A210445 A210446 A210447 KEYWORD nonn AUTHOR Zhi-Wei Sun, Jan 20 2013 STATUS approved

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Last modified June 19 18:32 EDT 2024. Contains 373507 sequences. (Running on oeis4.)