The Fibonacci sequence is defined by the recurrence relation:

F_n = F_n1 + F_n2, where F₁ = 1 and F₂ = 1.

Hence the first 12 terms will be:

F₁ = 1
F₂ = 1
F₃ = 2
F₄ = 3
F₅ = 5
F₆ = 8
F₇ = 13
F₈ = 21
F₉ = 34
F₁₀ = 55
F₁₁ = 89
F₁₂ = 144

The 12th term, F₁₂, is the first term to contain three digits.

What is the first term in the Fibonacci sequence to contain 1000 digits?

+-;fibo
(defn fibo []
  (map first 
    (iterate 
      (fn [[a b]]
        [b (+ a b)])
      [0 1]
    )
  )
)

(defn p25 []
  (println
    (count (take-while #(< (count (str %)) 1000) (fibo)))
  )
)

+-%pow
pow(_,0)->1;
pow(1,_)->1;
pow(A,B)->pow(A,B,1).
pow(_,0,Res)->Res;
pow(Mult,B,Res) when B band 1 == 1 ->
	pow(Mult*Mult,B bsr 1, Res*Mult);
pow(Mult,B,Res)->pow(Mult*Mult,B bsr 1, Res).

p25()->io:format("~w~n",[p25(0,1,pow(10,999),1)]).
p25(_,B,Limit,I) when B >= Limit ->I;
p25(A,B,Limit,I)->p25(B,A+B,Limit,I+1).

def p25
  limit=10**999
  a,b,i=0,1,1
  a,b,i=b,a+b,i+1 while b<limit
  puts i
end