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%I #9 May 23 2024 16:12:02
%S 11,23,7,827,41,19,7,1282187,2566561,1163,7,79,41,167,7,11,17,17,7,29,
%T 41,209715210460353203,7,838860894143178827,2566561,11,7,35393,29,179,
%U 7,19,673,85899345925559060566555523,7,47,41,29,7,661,5441,79,7,23
%N a(n) is the least prime factor of the concatenation of 2^n and 3^n.
%C a(n) = 7 if 3^n has d digits where 3^d + 5^n == 0 (mod 7).
%C a(n) is the concatenation of 2^n and 3^n if n is in A268111.
%e a(5) = 19 because the concatenation of 2^5 and 3^5 is 32243 = 19 * 1697.
%p f:= proc(n) local b, v, F;
%p b:= 3^n;
%p v:= 2^n*10^(1+ilog10(b)) + b;
%p F:= select(type,ifactors(v,easy)[2][..,1],integer);
%p if F <> [] then return min(F) fi;
%p min(ifactors(v)[2][...,1]);
%p end proc;
%p map(f, [$0..90]);
%Y Cf. A000079, A000244, A268111.
%K nonn,base
%O 0,1
%A _Robert Israel_, Jul 12 2023
%E Duplicated terms (former a(11)-a(20)) removed by _Georg Fischer_, May 23 2024
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