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Numbers k of the form 2*10^m + 2 such that 10^k + 9 is prime.
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%I #38 Jan 14 2017 16:28:47

%S 4,22,202

%N Numbers k of the form 2*10^m + 2 such that 10^k + 9 is prime.

%C Let k=2*10^(n-1)+2, then a(n)=10^k+9. For all k>4, k is a term of A058441.

%C The only known terms from A088275 (Numbers n such that 10^n + 9 is prime) that are of the form 2*10^j + 2 are 4, 22, and 202; given the lower bound given for that sequence's next term, a(4) >= 200002. - _Jon E. Schoenfield_, Jan 11 2017

%C For n<4, let k=a(n) and p=(10^k-9)/10^(k/2)+3=10^(k/2)+3, then p is prime. - _Sergey Pavlov_, Jan 13 2017

%F Numbers k of the form 2*10^m + 2 such that 10^k + 9 is prime.

%e For n=1, a(1)=4 and 10^4 + 9 is prime.

%Y Cf. A043037, A058441, A088275, A144249, A205529.

%K nonn,hard,bref,more

%O 1,1

%A _Sergey Pavlov_, Jan 08 2017