A089948 Smallest prime factor of the concatenation of the first n odd primes.

3, 5, 3, 13, 3, 23, 3, 11, 7, 13, 3, 137, 3, 19, 41, 3, 29, 1087, 7, 23, 3, 641, 7, 79, 124516914725653, 1254907, 983, 691, 19, 9656610616812422838401, 11, 3, 19, 3, 4951, 83404036302541, 3, 372707, 53, 3, 17, 3, 6073, 3, 11, 37, 3

Offset: 1

Author

Cino Hilliard, Jan 11 2004

Keywords

• nonn
• base

Comments

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.

Crossrefs

Cf. A089933.

Programs

Mathematica

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

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]",") ) }

Extensions

Edited and extended by Charles R Greathouse IV, Apr 29 2010