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A066481 Largest anti-divisor of n. 4
2, 3, 3, 4, 5, 5, 6, 7, 7, 8, 9, 9, 10, 11, 11, 12, 13, 13, 14, 15, 15, 16, 17, 17, 18, 19, 19, 20, 21, 21, 22, 23, 23, 24, 25, 25, 26, 27, 27, 28, 29, 29, 30, 31, 31, 32, 33, 33, 34, 35, 35, 36, 37, 37, 38, 39, 39, 40, 41, 41, 42, 43, 43, 44, 45, 45, 46, 47, 47, 48, 49, 49, 50 (list; graph; refs; listen; history; text; internal format)
OFFSET

3,1

COMMENTS

Apart from initial terms this is identical to A004396.

See A066272 for definition of anti-divisor.

LINKS

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

MAPLE

antidivisors := proc(n)

   local a, k;

   a := {} ;

   for k from 2 to n-1 do

      if abs((n mod k)- k/2) < 1 then

         a := a union {k} ;

      end if;

   end do:

   a ;

end proc:

A066481 := proc(n)

if n < 3 then

    return 0;

else

    sort(convert(antidivisors(n), list)) ;

    op(-1, %) ;

end if;

end proc: # R. J. Mathar, Mar 15 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 & ]; Table[ Last[ antid[n]], {n, 3, 100} ]

PROG

(PARI) a(n)=2*n\/3 \\ Charles R Greathouse IV, Feb 27 2013

CROSSREFS

Cf. A066482.

Sequence in context: A168052 A131737 A004396 * A248103 A121928 A175406

Adjacent sequences:  A066478 A066479 A066480 * A066482 A066483 A066484

KEYWORD

nonn

AUTHOR

Robert G. Wilson v, Jan 02 2002

STATUS

approved

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Last modified November 15 01:25 EST 2019. Contains 329143 sequences. (Running on oeis4.)