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A086571 a(1)=1, for n>1: a(n) = smallest divisor of n occurring earlier at most once.

%I A086571 #8 May 28 2015 21:18:53
%S A086571 1,1,3,2,5,2,7,4,3,5,11,4,13,7,15,8,17,6,19,10,21,11,23,6,25,13,9,14,
%T A086571 29,10,31,8,33,17,35,9,37,19,39,20,41,14,43,22,15,23,47,12,49,25,51,
%U A086571 26,53,18,55,28,57,29,59,12,61,31,21,16,65,22,67,34,69,35,71,18,73
%N A086571 a(1)=1, for n>1: a(n) = smallest divisor of n occurring earlier at most once.
%C A086571 a(A086939(n)) = a(A086938(n)) = n. - _Reinhard Zumkeller_, Jul 24 2003
%H A086571 Ivan Neretin, <a href="/A086571/b086571.txt">Table of n, a(n) for n = 1..10000</a>
%e A086571 a(p) = p for primes p>2;
%e A086571 divisor set of n=12: {1,2,3,4,6,12}, divisors occurring <12: 1=a(1)=a(2), 2=a(4)=a(6), 3=a(3)=a(9) and 4=a(8); as 4 occurs only once a(12)=4.
%t A086571 a = {1}; twice = {}; Do[nxt = Complement[Divisors[n], twice][[1]]; If[MemberQ[a, nxt], AppendTo[twice, nxt]]; AppendTo[a, nxt], {n, 2, 10}]; a (* _Ivan Neretin_, May 28 2015 *)
%Y A086571 Cf. A086572, A086938, A086939.
%K A086571 nonn
%O A086571 1,3
%A A086571 _Reinhard Zumkeller_, Jul 22 2003