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%I #30 May 19 2017 04:06:40
%S 0,1,3,4,5,17,29,31,53,59,101,277,647,1061,2381,2833,3613,3853,3929,
%T 5297,7417,90217,122219,173191,256199,336353,485977,591827,1059503
%N Exactly one of 3^n +- 2^n is prime.
%C Either (but not both) of 3^n - 2^n and 3^n + 2^n is prime. - _Harvey P. Dale_, Sep 16 2016
%C If 3^n + 2^n is prime then n must be a power of 2, and 3^n + 2^n is a generalized Fermat prime. It is conjectured that 3^n + 2^n is prime only for n=1,2,4: see A082101. - _Robert Israel_, Mar 15 2017, edited May 18 2017.
%e a(1)=0 because 3^0 - 2^0 = 0 = nonprime and 3^0 + 2^0 = 2 = prime;
%e a(2)=1 because 3^1 - 2^1 = 1 = nonprime and 3^1 + 2^1 = 5 = prime;
%e a(3)=3 because 3^3 - 2^3 = 19 = prime and 3^3 + 2^3 = 35 = nonprime.
%t epQ[n_]:=Module[{a=3^n,b=2^n},Sort[PrimeQ[{a+b,a-b}]]=={False,True}]; Select[Range[0,4000],epQ] (* _Harvey P. Dale_, Sep 16 2016 *)
%o (PARI) is(n)=isprime(3^n+2^n)+isprime(3^n-2^n)==1 \\ _Charles R Greathouse IV_, Mar 19 2017
%Y Cf. A283653, A082101, A057468.
%K nonn
%O 1,3
%A _Juri-Stepan Gerasimov_, Mar 15 2010
%E 9 and 11 removed by _R. J. Mathar_, Mar 29 2010
%E More terms from _Harvey P. Dale_, Sep 16 2016
%E a(20) from _Robert G. Wilson v_, Mar 15 2017
%E a(21) to a(29) (using data from A057468) from _Robert Israel_, May 18 2017
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