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A128028
Numbers k such that (13^k - 3^k)/10 is prime.
30
7, 31, 41, 269, 283, 7333, 8803
OFFSET
1,1
COMMENTS
All terms are primes.
No other terms exist < 100000.
MATHEMATICA
k=10; Select[ Prime[ Range[1, 200] ], PrimeQ[ ((k+3)^# - 3^#)/k ]& ]
PROG
(PARI) is(n)=isprime((13^n-3^n)/10) \\ Charles R Greathouse IV, Feb 17 2017
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, A128026, A128027, A128029, A128030, A128031, A128032.
Sequence in context: A276741 A000696 A171733 * A000921 A185004 A172490
KEYWORD
hard,more,nonn
AUTHOR
Alexander Adamchuk, Feb 11 2007
EXTENSIONS
One more term from Farideh Firoozbakht, Apr 03 2007
a(7)=8803 from Robert Price, Aug 12 2011
STATUS
approved