A089948 - OEIS

%I #10 Oct 01 2013 17:57:56

%S 3,5,3,13,3,23,3,11,7,13,3,137,3,19,41,3,29,1087,7,23,3,641,7,79,

%T 124516914725653,1254907,983,691,19,9656610616812422838401,11,3,19,3,

%U 4951,83404036302541,3,372707,53,3,17,3,6073,3,11,37,3

%N Smallest prime factor of the concatenation of the first n odd primes.

%C 3 is the only number < 10000 whose concatenation of odd primes is prime. Conjecture: Beyond 3 the concatenation of odd primes produce only composite numbers.

%t Join[{x=3},Table[First[First/@FactorInteger[x=FromDigits[Flatten[IntegerDigits[{x,Prime[n]}]]]]],{n,3,30}]] (* _Jayanta Basu_, Jun 04 2013 *)

%o (PARI) factorconcat(n) = { y=""; forprime(x=3,n, y=concat(Str(y),Str(x)); z=eval(y); a = component(factor(z),1); print1(a[1]",") ) }

%Y Cf. A089933.

%K nonn,base

%O 1,1

%A _Cino Hilliard_, Jan 11 2004

%E Edited and extended by _Charles R Greathouse IV_, Apr 29 2010