2012/2/5 Bartosz Dziewoski <matma.rex / gmail.com>:
> I hope this is not homework. For example this would work:
>
> def f n # this function calculates next number in your sequence
>    if n % 2 == 0 # n is even
>        return n / 2
>    else
>        return n * 3
>    end
> end
>
> num = gets.to_i # read in a number
> while true # infinitely...
>    num = f(num) # find the next number
>    puts num # print it
>    sleep 1 # wait one second
> end

There's also Integer#even? and #odd?.
e.g.
if n.even?
  return n / 2
else
  return n * 3
end