%I A020639
%S A020639 1,2,3,2,5,2,7,2,3,2,11,2,13,2,3,2,17,2,19,2,3,2,23,2,5,2,3,2,29,2,31,
               2,3,
%T A020639 2,5,2,37,2,3,2,41,2,43,2,3,2,47,2,7,2,3,2,53,2,5,2,3,2,59,2,61,2,3,2,
               5,
%U A020639 2,67,2,3,2,71,2,73,2,3,2,7,2,79,2,3,2,83,2,5,2,3,2,89,2,7,2,3,2,5,2,97
%N A020639 Lpf(n): least prime dividing n (a(1)=1).
%C A020639 a(1) = 1, a(2) = (2*1)/1 = 2; a(n+1) = a(n)*(the smallest prime divisor 
               of (n+1) divided by the largest prime divisor of a(n)). - Amarnath 
               Murthy (amarnath_murthy(AT)yahoo.com), Nov 28 2004
%C A020639 a(n) = the maximum number of integers such that all pairwise differences 
               are coprime to n. - Max Alekseyev (maxale(AT)gmail.com), Mar 17 2006
%C A020639 Also, except for the first term, the smallest prime dividing n. - Cino 
               Hilliard (pseudo.t(AT)comcast.net), Dec 08 2006
%D A020639 D. S. Mitrinovic et al., Handbook of Number Theory, Kluwer, Section IV.1.
%H A020639 Daniel Forgues, <a href="b020639.txt">Table of n, a(n) for n=1..100000</
               a>
%H A020639 Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/
               LeastPrimeFactor.html">Link to a section of The World of Mathematics.</
               a>
%F A020639 A014673(n) = a(A032742(n)); A117357(n) = a(A054576(n)). - Reinhard Zumkeller 
               (reinhard.zumkeller(AT)gmail.com), Mar 10 2006
%F A020639 A028233(n) = a(n)^A067029(n). - Reinhard Zumkeller (reinhard.zumkeller(AT)gmail.com), 
               May 13 2006
%o A020639 (PARI) g(n) = for(x=2,n,a=Vec(factor(x));print1(a[1][1]",")) - Cino Hilliard 
               (pseudo.t(AT)comcast.net), Dec 08 2006
%Y A020639 Cf. A090368 (bisection).
%Y A020639 Cf. A009190, A006530, A034684, A028233, A034699, A053585. See also A046669, 
               A032742.
%Y A020639 Cf. A068319, A088377.
%Y A020639 Sequence in context: A086286 A135679 A092028 this_sequence A092067 A079879 
               A071889
%Y A020639 Adjacent sequences: A020636 A020637 A020638 this_sequence A020640 A020641 
               A020642
%K A020639 nonn,easy,nice
%O A020639 1,2
%A A020639 David W. Wilson (davidwwilson(AT)comcast.net)