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A128026
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Numbers n such that (10^n - 3^n)/7 is prime.
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20
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OFFSET
| 1,1
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COMMENTS
| All terms are primes.
No other terms <100,000.
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MATHEMATICA
| k=7; Select[ Prime[ Range[1, 200] ], PrimeQ[ ((k+3)^# - 3^#)/k ]& ]
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PROG
| (PARI) forprime(p=2, 1e4, if(ispseudoprime((10^p-3^p)/7), print1(p", "))) \\ Charles R Greathouse IV, Jun 05, 2011
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CROSSREFS
| Cf. A028491 = numbers n such that (3^n - 1)/2 is prime. Cf. A057468 = numbers n such that 3^n - 2^n is prime. Cf. A059801 = numbers n such that 4^n - 3^n is prime. Cf. A121877 = numbers n such that (5^n - 3^n)/2 is a prime. Cf. A128024, A128025, A128027, A128028, A128029, A128030, A128031, A128032.
Sequence in context: A041977 A089213 A029499 * A041443 A057775 A088483
Adjacent sequences: A128023 A128024 A128025 * A128027 A128028 A128029
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KEYWORD
| hard,nonn
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AUTHOR
| Alexander Adamchuk (alex(AT)kolmogorov.com), Feb 11 2007
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EXTENSIONS
| a(6)-a(7) from Robert Price (pamandbobprice(AT)yahoo.com), Jun 04 2011
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