A066469 Numbers having exactly four anti-divisors.

13, 18, 40, 41, 61, 84, 100, 169, 289, 421, 784, 1024, 1104, 1296, 3121, 5776, 9216, 12544, 12769, 13924, 16129, 17956, 24649, 32761, 33024, 35344, 36721, 36864, 38809, 71821, 75076, 106261, 110224, 119716, 135721, 147456, 167281, 175561, 199081, 232324, 237169

Offset

1,1

Comments

See A066272 for definition of anti-divisor.

Links

Chai Wah Wu, Table of n, a(n) for n = 1..500

Jon Perry, The Anti-Divisor

Jon Perry, The Anti-divisor [Cached copy]

Jon Perry, The Anti-divisor: Even More Anti-Divisors [Cached copy]

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 & ]]; Select[ Range[10^5], Length[ antid[ # ]] == 4 & ]

Prog

(Python)
from sympy.ntheory.factor_ import antidivisor_count
A066469_list = [n for n in range(1, 10**3) if antidivisor_count(n) == 4] # Chai Wah Wu, Aug 02 2015

Crossrefs

Cf. A066272.

Sequence in context: A317771 A037158 A318080 * A318348 A197704 A218626

Adjacent sequences: A066466 A066467 A066468 * A066470 A066471 A066472

Keyword

nonn

Author

Robert G. Wilson v, Jan 02 2002

Extensions

More terms from Chai Wah Wu, Aug 02 2015

Status

approved