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A168535 Primes in A028359. 0


%S 2,1212121,12121212121,1212121212121212121212121212121212121212121

%N Primes in A028359.

%C Except for the first term, each term must both begin and end with a "1" because each term greater than 2 must end in a "1" and if a term begins with a "2" the sum of the digits of the term will be divisible by 3 and thus the term is not a prime. - _Harvey P. Dale_, Jun 22 2019

%C The next term (a(5)) has 139 digits and a(6) has 627 digits. - _Harvey P. Dale_, Jun 22 2019

%t Join[{2},Select[Table[FromDigits[PadRight[{},2n+1,{1,2}]],{n,30}],PrimeQ]] (* _Harvey P. Dale_, Jun 22 2019 *)

%Y Cf. A028359.

%K nonn

%O 1,1

%A _Zak Seidov_, Nov 28 2009

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Last modified December 4 13:29 EST 2021. Contains 349526 sequences. (Running on oeis4.)