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A128024
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Numbers n such that (7^n - 3^n)/4 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=4; Select[ Prime[ Range[1, 200] ], PrimeQ[ ((k+3)^# - 3^#)/k ]& ]
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PROG
| (PARI) forprime(p=3, 1e5, if(ispseudoprime((7^p-3^p)/4), print1(p", "))) \\ Charles R Greathouse IV, Jun 01 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. A128025, A128026, A128027, A128028, A128029, A128030, A128031, A128032.
Sequence in context: A163571 A146037 A172514 * A075487 A118128 A113875
Adjacent sequences: A128021 A128022 A128023 * A128025 A128026 A128027
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KEYWORD
| hard,more,nonn
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AUTHOR
| Alexander Adamchuk (alex(AT)kolmogorov.com), Feb 11 2007
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EXTENSIONS
| a(8)-a(9) from Farideh Firoozbakht (mymontain(AT)yahoo.com), Apr 08 2007
a(10) from Robert Price (pamandbobprice(AT)yahoo.com), Jun 01 2011
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