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

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

Offset

1,1

Links

Alois P. Heinz, Table of n, a(n) for n = 1..164

R. Ondrejka, Letter to N. J. A. Sloane, May 15 1976

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

Crossrefs

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

Sequence in context: A265688 A138146 A100706 * A262629 A111864 A098034

Adjacent sequences: A259099 A259100 A259101 * A259103 A259104 A259105

Keyword

nonn,base

Author

N. J. A. Sloane, Jun 23 2015

Status

approved