OFFSET
1,2
LINKS
EXAMPLE
The continued fractions for sqrt(3..8) are:
3 1;1,2
4 2 (square)
5 2;4
6 2;2,4
7 2;1,1,1,4
8 2;1,4
Those for 3, 6 and 8 have a period of 2, therefore the sequence starts with 1, 2, 1.
MAPLE
s := proc(n) if not issqr(n) then numtheory[cfrac](sqrt(n), 'periodic', 'quotients')[2]; if nops(%) = 2 then return %[1] fi fi; NULL end:
seq(s(n), n=1..399); # Peter Luschny, Jul 01 2019
MATHEMATICA
Reap[For[k = 3, k <= 399, k++, If[!IntegerQ[Sqrt[k]], cf = ContinuedFraction[Sqrt[k]]; If[Length[cf[[2]]] == 2, Sow[cf[[2, 1]]]]]]][[2, 1]] (* Jean-François Alcover, May 03 2024 *)
(* Second program (much simpler): *)
Table[2 a/b, {a, 1, 20}, {b, Rest@Divisors[2 a]}] // Flatten (* Jean-François Alcover, May 04 2024, after a remark by Kevin Ryde *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Georg Fischer, Jun 24 2019
STATUS
approved