A162489 - OEIS

%I #6 Aug 01 2015 21:31:19

%S 2,2,2,2,5,15,2,33,7,3,21,8,34,9,80,56,67,9,32,65,45,133,98,36,51,157,

%T 76,214,200,87,91,111,122,342,20,142,364,289,9,184,98,423,365,20,56,

%U 441,329,8,234,234,157,291,91,379,98,464,518,325,32,654,87,634,34,21,443

%N Least y such that x^y + y^x is prime, for x = A162488(n).

%C Sequences A162488 and A162490 list the corresponding x values and primes.

%C See there and the main entry A094133 for more information, links and references.

%F a(n)^A162488(n)+A162488(n)^a(n) = A162490(n)

%e The least x such that x^y + y^x is prime for some x>y>1 is A162488(1)=3, the smallest such y is a(1)=2, yielding the prime A162490(1) = 9 + 8 = 17.

%t lst = {}; Do[ If[ PrimeQ[x^y + y^x], AppendTo[lst, {x, y}]], {x, 3, 750}, {y, 2, x - 1}]; Transpose[ lst][[2]] (* _Robert G. Wilson v_, Aug 17 2009 *)

%o (PARI) for(i=3,999,for(j=2,i-1,isprime(i^j+j^i)|next;print1(j", ");break))

%Y Cf. A094133, A162486 - A162490.

%K nonn

%O 1,1

%A _M. F. Hasler_, Jul 04 2009

%E More terms from _Robert G. Wilson v_, Aug 17 2009