OFFSET
1,3
COMMENTS
Indices of primes in A205646.
a(50) > 10^6. - Robert Price, Oct 28 2020
FORMULA
EXAMPLE
57 is in the sequence because (3^57) + 16 = 1570042899082081611640534579 is prime.
MATHEMATICA
Select[Range[0, 2000], PrimeQ[3^# + 16] &] (* T. D. Noe, Jan 30 2012 *)
PROG
(PARI) is(n)=isprime(3^n+16) \\ Charles R Greathouse IV, Feb 17 2017
CROSSREFS
KEYWORD
nonn,hard,more
AUTHOR
Jonathan Vos Post, Jan 30 2012
EXTENSIONS
5319 from Nicolas M. Perrault, Nov 10 2012
a(30)-a(40) from Robert Price, Oct 23 2013
a(41) discovered by Lelio R Paula, November 2016
a(42)-a(43) from Robert Price, Apr 02 2020
a(44)-a(46) from Robert Price, May 14 2020
a(47)-a(49) from Robert Price, Oct 28 2020
STATUS
approved