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A287355 Order of largest subset of the positive rationals with neither the sum of numerators nor of denominators exceeding n. 0
1, 1, 2, 3, 3, 3, 4, 5, 5, 5, 6, 6, 7, 7, 7, 8, 8, 9, 9, 9, 9, 10, 10, 11, 11, 11, 11, 12, 12, 12, 13, 13, 13, 13, 14, 14, 14, 15, 15, 15, 15, 16, 16, 16, 17, 17, 17, 17, 17, 18 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

LINKS

Table of n, a(n) for n=1..50.

EXAMPLE

For n = 1, the largest subset is { 1/1 }, so a(1) = 1; for n = 2, the same; for n = 3, largest subsets are { 1/1, 2/1 } and { 1/2, 1/1 }, so a(3) = 2; for n = 4, the largest subset is { 1/2, 1/1, 2/1 }, so a(4) = 3; ...; for n = 16, the largest subset is { 1/4, 1/3, 1/2, 2/3, 1/1, 2/1, 3/1, 4/1 } (or swap 2/3 for 3/2), so a(16)=8, etc.

PROG

(Haskell)

f = go 0 2

  where

    go a r n

      | n >= c             = go (a+t) (r+1) (n-c)

      | n >= r*div n r + m = a + 2*div n r + 1

      | n >= r*div n r + m' + 1 = a + 2*div n r + 1

      | otherwise          = a + 2*div n r

      where

        t  = totient r

        c  = div (r*t) 2

        m  = midnum r

        m' = midnum (r-1)

    midnum r = head [a|a<-[div (r+1) 2..], gcd a r==1]

CROSSREFS

Sequence in context: A238516 A282692 A269371 * A194171 A004525 A049206

Adjacent sequences:  A287352 A287353 A287354 * A287356 A287357 A287358

KEYWORD

nonn

AUTHOR

Carl Edman, May 23 2017

STATUS

approved

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Last modified February 16 21:59 EST 2019. Contains 320200 sequences. (Running on oeis4.)