A066482 The smallest anti-divisor of n.

2, 3, 2, 4, 2, 3, 2, 3, 2, 5, 2, 3, 2, 3, 2, 4, 2, 3, 2, 3, 2, 7, 2, 3, 2, 3, 2, 4, 2, 3, 2, 3, 2, 8, 2, 3, 2, 3, 2, 4, 2, 3, 2, 3, 2, 5, 2, 3, 2, 3, 2, 4, 2, 3, 2, 3, 2, 7, 2, 3, 2, 3, 2, 4, 2, 3, 2, 3, 2, 5, 2, 3, 2, 3, 2, 4, 2, 3, 2, 3, 2, 8, 2, 3, 2, 3, 2, 4, 2, 3, 2, 3, 2, 64, 2, 3, 2, 3

Offset: 3

Author

Robert G. Wilson v, Jan 02 2002

Keywords

• nonn

Comments

Almost identical to A007978, least non-divisor of n, but there are some subtle differences.

See A066272 for definition of anti-divisor.

Links

• Seiichi Manyama, Table of n, a(n) for n = 3..10000

Crossrefs

Cf. A066481.

Programs

Mathematica

antid[n_] := Select[ Union[ Join[ Select[ Divisors[2n - 1], OddQ[ # ] && # != 1 &], Select[ Divisors[2n + 1], OddQ[ # ] && # != 1 &], 2n/Select[ Divisors[2*n], OddQ[ # ] && # != 1 &]]], # < n & ]; Table[ First[ antid[n]], {n, 3, 100} ]