A138861 Primes of form 10^n + 21.

31, 1021, 1000000021, 100000000000000021, 10000000000000000000000000000000000000000000000000000021, 100000000000000000000000000000000000000000000000000000000000000000000000000021

Offset

1,1

Comments

The next term has 134 digits. - Harvey P. Dale, Jan 15 2017

Links

Table of n, a(n) for n=1..6.

Mathematica

a={}; Do[p=10^n+21; If[PrimeQ[p], AppendTo[a, p]], {n, 0, 10^2}]; Print[a];
Join[{31}, Select[Table[100FromDigits[PadRight[{1}, n, 0]]+21, {n, 150}], PrimeQ]] (* Harvey P. Dale, Jan 15 2017 *)

Prog

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

Crossrefs

Cf. A108050.

Sequence in context: A154808 A307588 A218285 * A015257 A199234 A123826

Adjacent sequences: A138858 A138859 A138860 * A138862 A138863 A138864

Keyword

nonn

Author

Vladimir Joseph Stephan Orlovsky, May 16 2008

Status

approved