Greplin challenge p2

fib.rb

def fib(n)
  @a ||= [1,1]
  (0..n).each do |i|
    @a[i] = @a[i-1] + @a[i-2] unless @a[i]
  end
  @a[n]
end


def fib_after(n)
  f = 0
  i = 0
  while f <= n do
    f = fib(i)
    i += 1
  end
  return f
end

prime.rb

# not the most efficient prime detection
def prime?(n)
  2.upto(Math.sqrt(n)) do |d|
    return false if n % Float(d) == 0
  end
  return true
end

def prime_fib_after(n)
  f = fib_after(n)
  while !prime? f do
    f = fib_after(f)
  end
  return f
end

def prime_divisors(n)
  a = []
  2.upto(Math.sqrt(n)) do |d|
    a << d if n % Float(d) == 0 && prime?(d)
  end
  return a
end