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A128067 Numbers k such that (3^k + 7^k)/10 is prime. 9
3, 13, 31, 313, 3709, 7933, 14797, 30689, 38333 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

All terms are primes.

a(10) > 10^5. - Robert Price, Oct 03 2012

LINKS

Table of n, a(n) for n=1..9.

MATHEMATICA

k=7; Do[ p=Prime[n]; f=(3^p+k^p)/(k+3); If[ PrimeQ[f], Print[p]], {n, 1, 100} ]

PROG

(PARI) is(n)=isprime((3^n+7^n)/10) \\ Charles R Greathouse IV, Feb 17 2017

CROSSREFS

Cf. A007658 = numbers n such that (3^n + 1)/4 is prime. Cf. A057469 = numbers n such that (3^n + 2^n)/5 is prime. Cf. A122853 = numbers n such that (3^n + 5^n)/8 is prime. Cf. A128066, A128068, A128069, A128070, A128071, A128072, A128073, A128074, A128075. 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, A128028, A128029, A128030, A128031, A128032.

Sequence in context: A159047 A219971 A073337 * A052493 A279068 A247216

Adjacent sequences:  A128064 A128065 A128066 * A128068 A128069 A128070

KEYWORD

hard,more,nonn

AUTHOR

Alexander Adamchuk, Feb 14 2007

EXTENSIONS

More terms from Ryan Propper, Apr 02 2007

a(7)-a(9) from Robert Price, Oct 03 2012

STATUS

approved

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Last modified May 23 04:59 EDT 2019. Contains 323508 sequences. (Running on oeis4.)