This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A089948 #10 Oct 01 2013 17:57:56
%S A089948 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 A089948 124516914725653,1254907,983,691,19,9656610616812422838401,11,3,19,3,
%U A089948 4951,83404036302541,3,372707,53,3,17,3,6073,3,11,37,3
%N A089948 Smallest prime factor of the concatenation of the first n odd primes.
%C A089948 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 A089948 Join[{x=3},Table[First[First/@FactorInteger[x=FromDigits[Flatten[IntegerDigits[{x,Prime[n]}]]]]],{n,3,30}]] (* _Jayanta Basu_, Jun 04 2013 *)
%o A089948 (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 A089948 Cf. A089933.
%K A089948 nonn,base
%O A089948 1,1
%A A089948 _Cino Hilliard_, Jan 11 2004
%E A089948 Edited and extended by _Charles R Greathouse IV_, Apr 29 2010