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A128026 Numbers n such that (10^n - 3^n)/7 is prime. 29
2, 3, 5, 37, 599, 38393, 51431 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

All terms are primes.

No other terms < 100000.

LINKS

Table of n, a(n) for n=1..7.

MATHEMATICA

k=7; Select[ Prime[ Range[1, 200] ], PrimeQ[ ((k+3)^# - 3^#)/k ]& ]

PROG

(PARI) forprime(p=2, 1e4, if(ispseudoprime((10^p-3^p)/7), print1(p", "))) \\ Charles R Greathouse IV, Jun 05 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. A128024, A128025, A128027, A128028, A128029, A128030, A128031, A128032.

Sequence in context: A271387 A089213 A029499 * A041443 A057775 A215321

Adjacent sequences:  A128023 A128024 A128025 * A128027 A128028 A128029

KEYWORD

hard,nonn

AUTHOR

Alexander Adamchuk, Feb 11 2007

EXTENSIONS

a(6)-a(7) from Robert Price, Jun 04 2011

STATUS

approved

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Last modified May 19 07:05 EDT 2019. Contains 323386 sequences. (Running on oeis4.)