A083576 Least n-digit prime star number.

13, 181, 1093, 10333, 100621, 1040833, 10085473, 100000837, 1000705861, 10003758337, 100012479337, 1000001026513, 10000000794181, 100000078156441, 1000000776555301, 10000014919168441, 100000008716411701

Offset

2,1

Links

Robert Israel, Table of n, a(n) for n = 2..999

Maple

f:= proc(n) local i, t, s;
    t:= ceil(1/2 + sqrt(3+6*10^(n-1))/6);
    for i from t do
      s:= 6*i*(i-1)+1;
      if isprime(s) then return s fi
    od
end proc:
map(f, [$2..40]); # Robert Israel, Jun 12 2017

Mathematica

With[{psn=Select[Table[6n(n-1)+1, {n, 130*10^6}], PrimeQ]}, Table[ SelectFirst[ psn, IntegerLength[#]==k&], {k, 2, 18}]] (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, Apr 12 2020 *)

Prog

(PARI) star(n) = 6*n*(n-1)+1; L(n)=length(Str(n)); { stl(m)=print1(0", "); k=1; for(n=2, m, while(!isprime(star(k)) || L(star(k))!=n, k++); print1(star(k)", ")) }

Crossrefs

Cf. A003154 (star numbers).

Sequence in context: A127390 A142646 A201607 * A189432 A001570 A122571

Adjacent sequences: A083573 A083574 A083575 * A083577 A083578 A083579

Keyword

nonn,base

Author

Jason Earls, Jun 13 2003

Extensions

More terms from David Wasserman, Nov 23 2004

Status

approved