A211682 - OEIS

%I #15 Oct 08 2018 04:17:15

%S 2,3,5,7,23,37,53,73,373,237373,537373,5373737,53737373,53737373737,

%T 237373737373,737373737373737,53737373737373737,373737373737373737373,

%U 53737373737373737373737,53737373737373737373737373,373737373737373737373737373,5373737373737373737373737373737

%N Prime numbers such that all the substrings of length <= 2 are primes.

%C A211681 restricted to primes. Contains A085823. In contrast to A085823 this sequence seems to be not finite (conjecture).

%H Giovanni Resta, <a href="/A211682/b211682.txt">Table of n, a(n) for n = 1..36</a> (terms < 10^1000)

%e a(10)=237373, since all substrings of length <= 2 are primes (2, 3, 7, 23, 37, 73) and 237373 is prime.

%Y Cf. A085823, A019546, A046034, A211681.

%K nonn,base

%O 1,1

%A _Hieronymus Fischer_, Apr 30 2012

%E The originally submitted terms with index 20 and 21 are composite and have been erased therefore. - _Hieronymus Fischer_, Sep 24 2018

%E a(20)-a(22) from _Giovanni Resta_, Oct 08 2018