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 A138965 #4 Mar 31 2012 13:48:25 %S A138965 1,13,3,23,37,3,11617,5,3,135791113151719,29,3,5,11,3, %T A138965 135791113151719212325272931,17,3,7,13,3,131,5,3,11, %U A138965 25471443030907588399109,3,5,7,3,181,41,3,135791113151719212325272931333537394143454749515355575961636567,19,3,40351,5,3,7,11,3,5,57041,3,351269,11,3,135791113151719212325272931333537394143454749515355575961636567697173757779818385878991939597 %N A138965 Least prime factor of concatenation of first n odd numbers. %H A138965 Sean A. Irvine, <a href="/A138965/b138965.txt">Table of n, a(n) for n = 1..300</a> %H A138965 F. Smarandache, <a href="http://arXiv.org/abs/math/0604019">Sequences of numbers involved in unsolved problems, arXiv:math/0604019</a> %F A138965 A138965(n) = A020639(A019519(n)) (= 3 if n = 0 (mod 3)). %o A138965 (PARI) t=1; for( n=2,99, print1( factor( eval( t=Str( t,2*n-1 )))[1,1], ", ")) %Y A138965 Cf. A019519, A046036, A048847; A109837, A104644. %K A138965 base,nonn %O A138965 1,2 %A A138965 _M. F. Hasler_, Apr 14 2008