A128887 - OEIS

%I #5 Oct 01 2013 21:35:21

%S 5,17,71,99,123

%N Numbers n such that the number formed by the concatenation of the consecutive integers from 5 to n is prime.

%C Primes of this form are rare. 2 and 5 are the only beginning numbers less than 100 that form more than 2 primes for all ending numbers less than 1000.

%e The 2nd entry forms the number 567891011121314151617 which is prime.

%o (PARI) consecprimes(n,m) = { local(a,x,y); a=""; for(x=m,n, a=concat(a,Str(x)); y=eval(a); if(ispseudoprime(y), print(x","y) ) ) }

%K more,nonn,base

%O 1,1

%A _Cino Hilliard_, Apr 19 2007

%E Edited by _Charles R Greathouse IV_, Apr 25 2010