login
A181139
Numbers k such that R(k)^3 + R(k)^2 + 1 is prime, where R(k) = (10^k-1)/9.
0
1, 2, 3, 9, 41, 99, 1863, 4019, 8925
OFFSET
1,2
MATHEMATICA
okQ[n_]:=Module[{x=FromDigits[PadRight[{}, n, 1]]}, PrimeQ[x^3+x^2+1]]; Select[Range[5000], okQ] (* Harvey P. Dale, Nov 04 2011 *)
CROSSREFS
Sequence in context: A074428 A328436 A125052 * A162093 A052828 A214915
KEYWORD
nonn,hard,more
AUTHOR
Jason Earls, Oct 06 2010
EXTENSIONS
a(9) from Michael S. Branicky, Mar 22 2024
STATUS
approved