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A128024 Numbers n such that (7^n - 3^n)/4 is prime. 29
3, 7, 19, 109, 131, 607, 863, 2917, 5923, 12421 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

All terms are primes. No other terms < 100,000.

LINKS

Table of n, a(n) for n=1..10.

MATHEMATICA

k=4; Select[ Prime[ Range[1, 200] ], PrimeQ[ ((k+3)^# - 3^#)/k ]& ]

PROG

(PARI) forprime(p=3, 1e5, if(ispseudoprime((7^p-3^p)/4), print1(p", "))) \\ Charles R Greathouse IV, Jun 01 2011

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: A215487 A146037 A172514 * A245723 A118128 A113875

Adjacent sequences:  A128021 A128022 A128023 * A128025 A128026 A128027

KEYWORD

hard,more,nonn

AUTHOR

Alexander Adamchuk, Feb 11 2007

EXTENSIONS

a(8)-a(9) from Farideh Firoozbakht, Apr 08 2007

a(10) from Robert Price, Jun 01 2011

STATUS

approved

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Last modified May 24 01:29 EDT 2019. Contains 323528 sequences. (Running on oeis4.)