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A055520
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Numbers n such that 30*R_n + 1 is prime, where R_n = 11...1 is the repunit (A002275) of length n.
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3
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1, 2, 3, 4, 5, 6, 7, 17, 39, 49, 59, 77, 100, 150, 318, 381, 783, 1731, 1917, 8854, 11244, 11959, 12129, 18532, 22717, 23364, 24252, 24548, 25323, 30177, 53717, 380975, 424860
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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COMMENTS
| Also numbers n such that (10^(n+1)-7)/3 is prime.
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REFERENCES
| Martin Gardner, Strong Laws of Small Primes, in The Last Recreations, p. 194 (1997).
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LINKS
| Eric Weisstein's World of Mathematics, 3
Index entries for primes involving repunits
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MATHEMATICA
| Do[ If[ PrimeQ[30*(10^n - 1)/9 + 1], Print[n]], {n, 0, 50410}]
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CROSSREFS
| Equals A055557 minus 1.
Indices of A033175 that are primes. Cf. A051200, A055557.
Sequence in context: A171678 A039090 A138988 * A037342 A200333 A024644
Adjacent sequences: A055517 A055518 A055519 * A055521 A055522 A055523
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KEYWORD
| hard,nonn
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AUTHOR
| Eric Weisstein (eric(AT)weisstein.com)
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EXTENSIONS
| a(32)-a(33) from Leonid Durman, Jan 09-10 2012
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