power1.rb

require 'prime'

def power?(n)
    if n <= 0
        return false
    end

    if n == 1
        return true
    end

    ans = n.prime_division
    ans.size == 1 and ans[0][0] == 2
end

(1..1024).each do |n|
    puts n if power?(n)
end

power2.rb

def power?(n)
    if n <= 0
        return false
    end

    if n == 1
        return true
    end

    if n.odd?
        return false
    end

    ans = n
    while (ans /= 2) != 0
        return false if ans != 1 and ans.odd?
    end

    true
end

(1..1024).each do |n|
    puts n if power?(n)
end

power3.rb

def power?(n)
    if n <= 0
        false
    else
       (n & (n-1)) == 0
    end
end

(1..1024).each do |n|
    puts n if power?(n)
end