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

1,1

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.

Links

Table of n, a(n) for n=1..47.

Mathematica

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

Prog

(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]", ") ) }

Crossrefs

Cf. A089933.

Sequence in context: A049072 A059887 A023585 * A336806 A023583 A266603

Adjacent sequences: A089945 A089946 A089947 * A089949 A089950 A089951

Keyword

nonn,base

Author

Cino Hilliard, Jan 11 2004

Extensions

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

Status

approved