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A086571
a(1)=1, for n>1: a(n) = smallest divisor of n occurring earlier at most once.
10
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, 29, 10, 31, 8, 33, 17, 35, 9, 37, 19, 39, 20, 41, 14, 43, 22, 15, 23, 47, 12, 49, 25, 51, 26, 53, 18, 55, 28, 57, 29, 59, 12, 61, 31, 21, 16, 65, 22, 67, 34, 69, 35, 71, 18, 73
OFFSET
1,3
COMMENTS
a(A086939(n)) = a(A086938(n)) = n. - Reinhard Zumkeller, Jul 24 2003
LINKS
EXAMPLE
a(p) = p for primes p>2;
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.
MATHEMATICA
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 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Reinhard Zumkeller, Jul 22 2003
STATUS
approved