Divisibility properties of q-Fibonacci numbers Johann

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q q q q. q q q. q q q. +. + +. + + + +. + + + +. + +.. For. 1 q → we obviously get (1) ... p. F q. + is divisible by [ ]q p if p is any prime with. 2(mod 5). p ≡ ±. This.
Divisibility properties of q-Fibonacci numbers Johann Cigler Let q be a real number with 0  q  1 and let  Fn n0   0,1,1, 2,3,5,8, be the sequence of Fibonacci numbers. Define q  Fibonacci numbers by the recurrence Fn (q)  Fn 1 (q)  q n  2 Fn  2 (q) with initial values F0 (q)  0 and F1 (q)  1. The first terms are 0,1,1,1  q,1  q  q 2 ,1  q  q 2  q 3  q 4 ,1  q  q 2  q 3  2q 4  q 5  q 6 ,. For q  1 we obviously get Fn (1)  Fn . Let [n]  [n]q 

1  qn  1  q    q n 1. 1 q

It is known that Fp 1 (q) is divisible by [ p]q if p is any prime with p  2(mod 5). This result has been proposed as problem by George Andrews and has been solved by Leonard Carlitz (Fibonacci Quarterly 8 (1970), Problem H 138, p. 76-81). For example F4 (q)  [3]q and F8 (q )  [7]q 1  q 4  q 6  .

It is rather trivial that F5 n (q) is divisible by [5]q . To show this observe that q n  q n (mod 5) (mod[5]q ). Therefore F5 n (q )  0  mod[5]q  implies F5 n  2 (q)  F5 n 1 (q), F5 n 3 (q )  F5 n  2 (q ) 1  q   F5 n 1 (q ) 1  q  ,

F5 n  4 (q )  F5 n 3 (q )  q 2 F5 n  2 ( q )  1  q  q 2  F5 n 1 ( q ) and finally

F5 n 5 (q )  F5 n  4 (q )  q 3 F5 n 3 ( q )  1  q  q 2  q 3  q 5  F5 n 1 ( q )  0  mod[5]q  .

For example F10 (q )  [5]q 2 1  q  q 4 [9]q   [5]q 1  q  q 2  q 3  q 4 1  q  q 4 [9]q  . Thus F10 (q) is not only divisible by [5]q but even by 5q 2 . Computer experiments suggest the Conjecture

F5 n (q) is divisible by [5]qn and if n  5m then also by [5]qn [5]q . I would be interested in a proof or disproof of this conjecture.

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