cp's OEIS Frontend

A083576 Least n-digit prime star number.

%I A083576 #19 Apr 12 2020 13:31:42
%S A083576 13,181,1093,10333,100621,1040833,10085473,100000837,1000705861,
%T A083576 10003758337,100012479337,1000001026513,10000000794181,
%U A083576 100000078156441,1000000776555301,10000014919168441,100000008716411701
%N A083576 Least n-digit prime star number.
%H A083576 Robert Israel, <a href="/A083576/b083576.txt">Table of n, a(n) for n = 2..999</a>
%p A083576 f:= proc(n) local i,t,s;
%p A083576     t:= ceil(1/2 + sqrt(3+6*10^(n-1))/6);
%p A083576     for i from t do
%p A083576       s:= 6*i*(i-1)+1;
%p A083576       if isprime(s) then return s fi
%p A083576     od
%p A083576 end proc:
%p A083576 map(f, [$2..40]); # _Robert Israel_, Jun 12 2017
%t A083576 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 *)
%o A083576 (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)",")) }
%Y A083576 Cf. A003154 (star numbers).
%K A083576 nonn,base
%O A083576 2,1
%A A083576 _Jason Earls_, Jun 13 2003
%E A083576 More terms from _David Wasserman_, Nov 23 2004