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A101395
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Numbers n such that 4*10^n+7 is prime.
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1
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OFFSET
| 1,3
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COMMENTS
| No further terms < 50000.
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LINKS
| Makoto Kamada, Factorizations of 400...007.
Sabin Tabirca and Kieran Reynolds, Lacunary Prime Numbers.
Index entries for primes involving repunits.
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EXAMPLE
| n = 1, 3, 9 are members since 47, 4007 and 4000000007 are primes.
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MATHEMATICA
| Do[ If[ PrimeQ[4*10^n + 7], Print[n]], {n, 0, 10000}]
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CROSSREFS
| Cf. A056806, A100501, A088274.
Sequence in context: A090012 A079096 A143293 * A133189 A020092 A190341
Adjacent sequences: A101392 A101393 A101394 * A101396 A101397 A101398
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KEYWORD
| hard,nonn
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AUTHOR
| Julien Peter Benney (jpbenney(AT)ftml.net), Jan 15 2005
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