cp's OEIS Frontend

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

%I A259102 #16 Aug 15 2015 11:51:28
%S A259102 111,11111,1111111,11111111111,1111111111111,11111111111111111,
%T A259102 11111111111111111111111111111,1111111111111111111111111111111,
%U A259102 1111111111111111111111111111111111111,11111111111111111111111111111111111111111,1111111111111111111111111111111111111111111
%N A259102 Composite repunits with a prime number of 1's.
%H A259102 Alois P. Heinz, <a href="/A259102/b259102.txt">Table of n, a(n) for n = 1..164</a>
%H A259102 R. Ondrejka, <a href="/A000522/a000522.pdf">Letter to N. J. A. Sloane, May 15 1976</a>
%p A259102 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
%p A259102 # second Maple program:
%p A259102 r:= n-> (10^n-1)/9:
%p A259102 b:= proc(n) option remember; local p;
%p A259102       p:=`if`(n=1, 1, b(n-1));
%p A259102       do p:= nextprime(p);
%p A259102          if not isprime(r(p)) then return p fi
%p A259102       od
%p A259102     end:
%p A259102 a:= n-> r(b(n)):
%p A259102 seq(a(n), n=1..15);  # _Alois P. Heinz_, Jun 25 2015
%Y A259102 Cf. A002275, A004022, A004023, A031974, A179005.
%K A259102 nonn,base
%O A259102 1,1
%A A259102 _N. J. A. Sloane_, Jun 23 2015