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%I #3 Mar 31 2012 12:38:25
%S 2,3,4,5,7,8,11,13,15,17,19,23,26,30,42,47,53,65,73,77,84,92,100,101,
%T 106,110,116,120,122,122,124,133,137,163,167,173,173
%N Solutions x to the equation x^x-y^y = some prime number for any y.
%C These are the numbers a in the definition of A068146.
%C If there are two solutions, like with (x,y) = (17,12) and (x,y) = (17,16) with
%C the same x, only one instance of x is placed into the sequence, so there is no
%C 1-to-1 correspondence with terms in A068146.
%C The corresponding set of y contains at least the numbers 1 to 6, 10, 12, 14, 16, 17, 19, 20, 22 etc
%e Triples (x,y,prime) are (2,1,3), (3,2,23), (4,3,229), (5,2,3121), (7,6,776887),
%e (8,5,16774091), (11,10,275311670611), (13,6,302875106545597), (15,4,437893890380859119),
%e (17,12,827240252970236315921), (17,16,808793517812627212561) etc
%t f[a_,b_]:=a^a-b^b; lst={};Do[Do[If[a>b,p=f[a,b]];If[PrimeQ[p],AppendTo[lst, a]],{b,4*4!}],{a,5*4!}];Union[lst]
%Y Cf. A068146
%K nonn
%O 1,1
%A _Vladimir Joseph Stephan Orlovsky_, Jul 02 2009
%E Edited and extended by _R. J. Mathar_, Sep 16 2009