1,4

Where A162488 are numbers x such that x^y+y^x is prime, for some y>1, y<x and A162489 is least y such that x^y+y^x is prime, for x=A162488(n).

Table of n, a(n) for n=1..58.

a(1)=0 because 1^1+1^1=2=prime and 0=1-1; a(2)=1 because 1^2+2^1=3=prime and 1=2-1; a(3)=1 because 2^3+3^2 and 1=3-2; a(4)=7 because 2^9+9^2 and 7=9-2.

Cf. A094133, A162488, A162489.

Sequence in context: A107744 A254762 A275681 * A304995 A160007 A024613

Adjacent sequences: A173925 A173926 A173927 * A173929 A173930 A173931

nonn

Juri-Stepan Gerasimov, Mar 02 2010

a(30) and a(32) corrected by R. J. Mathar, Mar 09 2010

approved