A086571 - OEIS

A086571

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

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

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OFFSET

1,3

COMMENTS

a(A086939(n)) = a(A086938(n)) = n. - Reinhard Zumkeller, Jul 24 2003

LINKS

Ivan Neretin, Table of n, a(n) for n = 1..10000

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

Cf. A086572, A086938, A086939.

Sequence in context: A274457 A328579 A046524 * A350509 A133945 A124219

Adjacent sequences: A086568 A086569 A086570 * A086572 A086573 A086574

KEYWORD

nonn

AUTHOR

Reinhard Zumkeller, Jul 22 2003

STATUS

approved