

A279783


Denominator of Farey fractions sorted according to increasing k, with k = numerator^2 + denominator^2. Fractions with same k are sorted in order of increasing denominator.


5



1, 1, 2, 3, 3, 4, 4, 5, 5, 5, 6, 5, 7, 7, 7, 6, 7, 8, 8, 7, 9, 7, 9, 8, 9, 10, 9, 10, 8, 11, 11, 9, 11, 11, 9, 12, 11, 10, 11, 12, 11, 13, 13, 13, 10, 11, 13, 12, 13, 14, 11, 13, 14, 13, 11, 14, 15, 15, 13, 15, 13, 16, 12, 16, 13, 15, 14, 16, 15, 13, 17, 17, 17, 16, 17, 13, 17, 14, 17, 18, 16
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OFFSET

1,3


COMMENTS

The parameter k is the square of the Euclidean distance of the corresponding points to the origin in the "denominator, numerator" representation space.
The fractions in order begin: 0/1, 1/1, 1/2, 1/3, 2/3, 1/4, 3/4, 1/5, 2/5, 3/5, 1/6, 4/5, 1/7, 2/7, 3/7, 5/6, ..., .
Note that the fraction 2/4 is not in the above since it can be reduced to 1/2.


LINKS

Table of n, a(n) for n=1..81.


EXAMPLE

The point (1,0) lies closer to the origin than any other point in the first quadrant. Therefore a(1) = 1;
The next point is (1,1) because it lies closer to the origin. Therefore a(2) = 1;
The point (2,1) lies the next closest to the origin. Therefore a(3) = 2;
The point (3,1) is the next closest to the origin. Therefore a(4)= 3;
The point (3,2) is the next closest to the origin. Therefore a(5)= 3;
etc.


MATHEMATICA

nmax = 22; (* Maximum explorative denominator *)
fracs = Sort@Union@Flatten@Table[a/b, {b, nmax}, {a, 0, b}];
(* Sorting generated fractions according to increasing Euclidean distance first, and then by increasing denominator *)
fracsorted = SortBy[fracs, {(Numerator@#)^2 + (Denominator@#)^2 &,
Denominator@# &}];
nmaxlimit = Floor[nmax^2/4] (*Safe limit for a correctly sorted sequence*);
Take[Denominator@fracsorted, nmaxlimit]


CROSSREFS

Cf. A279782.
Sequence in context: A061091 A196241 A086592 * A132663 A306631 A023964
Adjacent sequences: A279780 A279781 A279782 * A279784 A279785 A279786


KEYWORD

nonn,frac


AUTHOR

Robert G. Wilson v and Andres Cicuttin, Dec 19 2016


STATUS

approved



