aptinio

(1...1000).to_a.select {|n| n.remainder(3) == 0 || n.remainder(5) == 0}.reduce(:+)

aptinio

fib = [1, 2]

def fib.next
  self[-1] + self[-2]
end

fib << fib.next while fib.next < 4_000_000

fib.select {|f| f.remainder(2) == 0}.reduce(:+)

aptinio

require 'mathn'
600851475143.prime_division.last.first

aptinio

def palindrome?(integer)
  string = integer.to_s
  string == string.reverse
end

products = []

999.step(100, -1).to_a.each do |a|
  999.step(100, -1).to_a.each do |b|
    product = a*b

aptinio

(1..20).to_a.reduce :lcm

aptinio

(1..100).to_a.reduce(:+)**2 - (1..100).to_a.reduce {|sum_of_squares, n| sum_of_squares + n**2}

aptinio

require 'mathn'

prime = Prime.new
10_000.times {prime.succ}
prime.succ

aptinio

numbers = <<EOS
73167176531330624919225119674426574742355349194934
96983520312774506326239578318016984801869478851843
85861560789112949495459501737958331952853208805511
12540698747158523863050715693290963295227443043557
66896648950445244523161731856403098711121722383113
62229893423380308135336276614282806444486645238749
30358907296290491560440772390713810515859307960866
70172427121883998797908792274921901699720888093776
65727333001053367881220235421809751254540594752243

aptinio

def pythagorean_triple(m, n)
  m, n = n, m if m > n
  [n**2 - m**2, 2*m*n, n**2 + m**2]
end

infinity = 1.0/0.0

catch :answer_found do
  (1..infinity).each do |m|
    (m+1..infinity).each do |n|

aptinio

require 'mathn'

Prime.new.inject(0) { |sum, n|
  break(sum) if n >= 2_000_000
  sum + n
}