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A065813
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Least m such that (p^(2*m+1)-1)/(p-1) is a prime, where p = prime(n).
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1
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1, 1, 1, 2, 8, 2, 1, 9, 2, 2, 3, 6, 1, 2, 63, 5, 1, 3, 9, 1, 2, 2, 2, 1, 8, 1, 9, 8, 8, 11, 2, 1, 5, 81, 3, 6, 8, 3, 1, 1, 9, 8, 8, 2, 15, 288, 20, 119, 2, 5, 56, 2, 8, 3, 11, 2
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,4
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LINKS
| Andy Steward, Prime Generalized Repunits
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EXAMPLE
| a(5) = 8 because ithprime(5) = 11, (11^(2*m+1)-1)/10 is not a prime for m = 1..7 and (11^17-1)/10 = 50544702849929377 is a prime.
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MATHEMATICA
| Do[p=Prime[w]; s=DivisorSigma[1, (p^r)^2]; z=DivisorSigma[0, (p^r)^2]; If[PrimeQ[s], Print[{p, r, p^r, s, z}]], {w, 1, 100}, {r, 1, 100}] For w=12, this prints out first {37, 6, 2565726409, 6765811783780036261, 13}.
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PROG
| (PARI) { allocatemem(932245000); for (n=1, 100, x=prime(n); s=x^2; q=x - 1; m=1; while (!isprime(((x*=s) - 1)/q), m++); write("b065813.txt", n, " ", m) ) } [From Harry J. Smith (hjsmithh(AT)sbcglobal.net), Oct 31 2009]
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CROSSREFS
| Cf. A000005, A000203, A000040, A065403-A065405, A000043, A001348, A065854.
Sequence in context: A087198 A200589 A194567 * A076344 A173686 A090975
Adjacent sequences: A065810 A065811 A065812 * A065814 A065815 A065816
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KEYWORD
| hard,nonn
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AUTHOR
| Vladeta Jovovic (vladeta(AT)eunet.rs) and Labos E. (labos(AT)ana.sote.hu), Nov 13 2001
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