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A076515
Numbers k such that 1 + 3^k + 5^k is prime.
5
0, 12, 36, 48, 72, 120, 605376
OFFSET
1,2
COMMENTS
Next term, if it exists, is greater than 35000. - Vaclav Kotesovec, Jan 26 2016
No more terms up to 75000 (previous range rechecked). All terms are multiples of 12: if k > 0 is not a multiple of 12, 1 + 3^k + 5^k is divisible by 3, 5 or 7. - Rick L. Shepherd, Aug 06 2017
Next term, if it exists, is greater than 10^6. - Jon Grantham, Jul 29 2023
MAPLE
A076515:=n->`if`(isprime(1+3^n+5^n), n, NULL): seq(A076515(n), n=0..200); # Wesley Ivan Hurt, Aug 06 2017
MATHEMATICA
Do[ If[ PrimeQ[1 + 3^n + 5^n], Print[n]], {n, 0, 3500, 2}]
Select[Range[0, 5000], PrimeQ[1+3^#+5^#]&] (* Harvey P. Dale, Mar 09 2012 *)
PROG
(Magma) [n: n in [0..1000]|IsPrime(3^n+5^n+1)] // Vincenzo Librandi, Jan 22 2011
(PARI) lista(nn) = for(n=0, nn, if(ispseudoprime(1 + 3^n + 5^n), print1(n, ", "))); \\ Altug Alkan, Jan 25 2016
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Zak Seidov, Oct 17 2002
EXTENSIONS
a(7) from Jon Grantham, Jul 29 2023
STATUS
approved