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%I #17 Jan 24 2017 20:40:52
%S 9,51,2403,5764803,33232930569603,1104427674243920646305299203
%N a(n) = 7^(2^n) + 2.
%C These numbers are divisible by 3. This follows by expanding the binomial (6+1)^(2^n) + 2 to get 6h + 1 + 2 for some h. Therefore 3 divides 7^(2^n) + 2.
%F a(n) = A165425(n+3) + 2. - _R. J. Mathar_, Sep 10 2016
%p A152580:=n->7^(2^n) + 2: seq(A152580(n), n=0..8); # _Wesley Ivan Hurt_, Jan 22 2017
%o (PARI) g(a,n) = if(a%2,b=2,b=1);for(x=0,n,y=a^(2^x)+b;print1(y","))
%o (PARI) a(n) = 7^(2^n) + 2; \\ _Michel Marcus_, Jan 24 2017
%Y Cf. A165425.
%K nonn,easy
%O 0,1
%A _Cino Hilliard_, Dec 08 2008
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