OFFSET
0,2
COMMENTS
a(n) is the least positive integer k such that one of the following holds:
(1) there is an integer J such that n*k^2 < J^2 < (n+1)*k^2; or
(2) there is an integer J such that (n+1)*k^2 = J^2.
Note that (1) is equivalent to the existence of a rational number H with denominator k such that n < H^2 < n+1.
Positions of 1: A005563.
Positions of 2: 2*A000217.
Positions of 2n+1: A000290.
LINKS
Hugo Pfoertner, Table of n, a(n) for n = 0..1000
Michael Weiss, On the Distribution of Rational Squares, arXiv:1510.07362 [math.NT], 2015.
Michael Weiss, Where Are the Rational Squares?, The American Mathematical Monthly, Vol. 124, No. 3 (March 2017), pp. 255-259.
EXAMPLE
The results are easily read from an array of k*sqrt(n),
represented here by approximations:
1.00 1.41 1.73 2.00 2.24 2.45 2.65
2.00 2.83 3.46 4.00 4.47 4.90 5.29
3.00 4.24 5.20 6.00 6.71 7.35 7.94
4.00 5.66 6.93 8.00 8.94 9.80 10.58
MATHEMATICA
Table[k = 1; While[Floor[k Sqrt[n + 1]] <= k Sqrt@ n, k++]; k, {n, 120}] (* Michael De Vlieger, Aug 14 2016 *)
PROG
(PARI) a(n) = my(k = 1); while(floor(k*sqrt(n+1)) <= k*sqrt(n), k++); k; \\ Michel Marcus, Oct 07 2017
CROSSREFS
KEYWORD
nonn
AUTHOR
Clark Kimberling, Dec 27 2010
EXTENSIONS
Added a(0)=1 and changed b-file by N. J. A. Sloane, Aug 16 2016
STATUS
approved