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