A138861 - OEIS

%I #6 Jan 15 2017 13:32:14

%S 31,1021,1000000021,100000000000000021,

%T 10000000000000000000000000000000000000000000000000000021,

%U 100000000000000000000000000000000000000000000000000000000000000000000000000021

%N Primes of form 10^n + 21.

%C The next term has 134 digits. - _Harvey P. Dale_, Jan 15 2017

%t a={};Do[p=10^n+21;If[PrimeQ[p],AppendTo[a,p]],{n,0,10^2}];Print[a];

%t Join[{31},Select[Table[100FromDigits[PadRight[{1},n,0]]+21,{n,150}],PrimeQ]] (* _Harvey P. Dale_, Jan 15 2017 *)

%o (PARI) for(n=1,1e3,if(ispseudoprime(t=10^n+21),print1(t", "))) \\ _Charles R Greathouse IV_, May 15 2013

%Y Cf. A108050.

%K nonn

%O 1,1

%A _Vladimir Joseph Stephan Orlovsky_, May 16 2008