A259102 Composite repunits with a prime number of 1's.

111, 11111, 1111111, 11111111111, 1111111111111, 11111111111111111, 11111111111111111111111111111, 1111111111111111111111111111111, 1111111111111111111111111111111111111, 11111111111111111111111111111111111111111, 1111111111111111111111111111111111111111111

Offset: 1

Author

N. J. A. Sloane, Jun 23 2015

Keywords

• nonn
• base

Links

• Alois P. Heinz, Table of n, a(n) for n = 1..164
• R. Ondrejka, Letter to N. J. A. Sloane, May 15 1976

Crossrefs

Cf. A002275, A004022, A004023, A031974, A179005.

Programs

Maple

f:=n->(10^n-1)/9; [f(3),f(5),f(7),f(11),f(13),f(17),f(29),f(31),f(37),f(41),f(43),f(47)];  # cf. A004023
# second Maple program:
r:= n-> (10^n-1)/9:
b:= proc(n) option remember; local p;
      p:=`if`(n=1, 1, b(n-1));
      do p:= nextprime(p);
         if not isprime(r(p)) then return p fi
      od
    end:
a:= n-> r(b(n)):
seq(a(n), n=1..15);  # Alois P. Heinz, Jun 25 2015