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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 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 24 07:53 EST 2020. Contains 338607 sequences. (Running on oeis4.)