lune-sta

p (1..501).map{|n|4*(2*n-3)**2+20*(n-1)}.inject{|a,b|a+b}-3 # 669171001

lune-sta

p (2..100).map{|a|(2..100).map{|b|a**b}}.flatten.uniq.size # 9183

lune-sta

p (0..999999).select{|a|a == a.to_s.split(//).map{|a|a.to_i**5}.inject{|a,b|a+b}}.inject{|a,b|a+b}-1 # 443839

lune-sta

$p = [1,2,5,10,20,50,100,200]
$ans = 0

def dfs(n)
  case n.inject{|a,b|a+b}
  when 0..199
    $p.each{|a|dfs(n<<a)}
  when 200
    $ans += 1
    p n

lune-sta

ans = 0
(0).step(200,100) do |p100|
  (0).step(200,50) do |p50|
    (0).step(200,20) do |p20|
      (0).step(200,10) do |p10|
        (0).step(200,5) do |p5|
          (0).step(200,2) do |p2|
            ans += 1 if p100+p50+p20+p10+p5+p2 <= 200
          end
        end

lune-sta

p (1000..9999).select{|a|(2..Math::sqrt(a)).select{|b|a % b == 0 && "#{a}#{b}#{a/b}".split(//).sort.join == (1..9).to_a.join}.empty?.!}.inject(0, :+) # 45228

lune-sta

ans = Rational(1, 1)
(1..9).each do |a|
  (1...a).each do |b|
    (1..9).each do |c|
      d = Rational(b,a)
      if Rational(b*10+c, a*10+c) == d ||
         Rational(b*10+c, a+c*10) == d ||
         Rational(b+c*10, a*10+c) == d ||
         Rational(b+c*10, a+c*10) == d
         ans *= d

lune-sta

require 'prime'
p Prime.each.lazy.select{|a|a>7&&(1...a.to_s.size).map{|b|[a.to_s[0,b],a.to_s.split(//).reverse.join[0,b].split(//).reverse.join]}.flatten.all?{|b|b.to_i.prime?}}.take(11).inject(:+)
# 748317 (ruby2.0.0dev)

lune-sta

p (3...(1..9).inject(1,:*)*9).select{|a|a==a.to_s.split(//).map{|b|(1..b.to_i).inject(1,:*)}.inject(0,:+)}.inject(0,:+) # 40730

lune-sta

require 'prime'
p Prime.each(10**6).select{|a|(1..a.to_s.size-1).map{|b|a.to_s.scan(/.{#{b}}|.+\Z/)}.map{|b|b.push(b.shift).join.to_i}.select{|b|b.prime?.!}.empty?}.size # 55