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A066468 Numbers having just three anti-divisors. 1
7, 10, 11, 14, 15, 19, 20, 21, 26, 29, 30, 34, 44, 48, 51, 54, 56, 69, 79, 89, 106, 114, 120, 134, 141, 146, 156, 174, 191, 216, 224, 244, 251, 271, 296, 309, 316, 321, 359, 376, 384, 386, 394, 404, 411, 439, 496, 516, 524, 596, 601, 614, 659, 664, 691, 719 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

See A066272 for definition of anti-divisor.

LINKS

Table of n, a(n) for n=1..56.

Jon Perry, The Anti-Divisor

Jon Perry, The Anti-divisor [Cached copy]

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

MAPLE

A066468:= proc(q)

local k, n, t;

for n from 1 to q do

t:=0; for k from 2 to n-1 do if abs((n mod k)-k/2)<1 then t:=t+1; fi; od;

if t=3 then print(n); fi; od; end:

A066468 (10^10); # Paolo P. Lava, Feb 22 2013

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[10^4], Length[ antid[ # ]] == 3 & ]

CROSSREFS

Cf. A066272.

Sequence in context: A191875 A194418 A094764 * A088769 A057986 A274204

Adjacent sequences:  A066465 A066466 A066467 * A066469 A066470 A066471

KEYWORD

nonn

AUTHOR

Robert G. Wilson v, Jan 02 2002

STATUS

approved

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Last modified July 14 10:29 EDT 2020. Contains 335721 sequences. (Running on oeis4.)