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
KEYWORD
nonn,base
AUTHOR
Jason Earls, Jun 13 2003
EXTENSIONS
More terms from David Wasserman, Nov 23 2004
STATUS
approved