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A056807
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Numbers n such that 3*10^n +1 is prime.
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5
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1, 3, 7, 10, 28, 36, 67, 81, 147, 483, 643, 1020, 1900, 2620, 10453, 27720, 52824
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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LINKS
| Makoto Kamada, Factorizations of 300...001
Sabin Tabirca and Kieran Reynolds, Lacunary Prime Numbers.
Primeform: User group for PFGW & PrimeForm programs.
Index entries for primes involving repunits.
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EXAMPLE
| n = 3 gives (3*10^3+1) = 3000+1 = 3001, which is prime.
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MATHEMATICA
| Do[ If[ PrimeQ[ 3*10^n + 1], Print[ n ]], {n, 0, 20000}]
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CROSSREFS
| Cf. A056797.
Sequence in context: A127277 A041437 A041525 * A146927 A193650 A041783
Adjacent sequences: A056804 A056805 A056806 * A056808 A056809 A056810
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KEYWORD
| nonn,hard
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AUTHOR
| Robert G. Wilson v (rgwv(AT)rgwv.com), Aug 22 2000
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EXTENSIONS
| a(13) & a(14) from Julien Peter Benney (jpbenney(AT)ftml.net), Nov 23 2004.
a(15) from Hugo Pfoertner.
a(16) & a(17) from Robert G. Wilson v (rgwv(AT)rgwv.com), Jan 18 2005
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