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%I #7 Nov 21 2013 12:49:59
%S 8,17,54,57,177,368,2169,2530,6250,8361,94932,131361,178478,524649,
%T 1596520,1647086,8389137,48989176,129145076,536871753,1162268326,
%U 1221074418,1996813914,2147484609,94143190994,96951758924,137438954841
%N Numbers of the form a^b+b^a, a and b are primes.
%C 2^2+2^2=8, 2^3+3^2=17, 3^3+3^3=54, 2^5+5^2=57, 2^7+7^2=177, 3^5+5^3=368,..
%t nMax=10^12; lim=PrimePi[Log[2, nMax]]; f[a_,b_]:=Prime[a]^Prime[b] + Prime[b]^Prime[a]; Select[Union[Flatten[Table[f[a,b], {a,lim}, {b,lim}]]], #<=nMax&]
%t nMax=10^12; lim=PrimePi[Log[2, nMax]]; Select[Union[First[#]^Last[#] + Last[#]^First[#]&/@ Tuples[Prime[Range[lim]],{2}]], #<=nMax&] (* _Harvey P. Dale_, Mar 12 2011 *)
%Y Cf. A076980, A173054, A173055.
%K nonn
%O 1,1
%A _Vladimir Joseph Stephan Orlovsky_, Feb 08 2010
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