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A138861 Primes of form 10^n + 21. 1
31, 1021, 1000000021, 100000000000000021, 10000000000000000000000000000000000000000000000000000021, 100000000000000000000000000000000000000000000000000000000000000000000000000021 (list; graph; refs; listen; history; text; internal format)
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

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Last modified November 20 17:09 EST 2019. Contains 329337 sequences. (Running on oeis4.)