lune-sta

y = 1901
m = 1
d = 1
w = 1 # 0..6 -> Sun..Sat
count = 0

def m31? (m)
  [1,3,5,7,8,10,12].each do |i|
    if m == i
      return true

lune-sta

require 'date'
st = Date::new(1901, 1, 1)
en = Date::new(2000, 12, 31)
count = 0
while st != en
  count += 1 if st.day == 1 && st.wday == 0
  st += 1
end
p count # 171

lune-sta

puts (1..100).inject(1){|a, b| a * b}.to_s.split(//).map(&:to_i).inject(0){|a, b| a + b} # 648

lune-sta

require 'prime'
arr = Array.new(10001){1}
sum = 0
2.upto(10000) do |i|
  i.prime_division.each do |j|
    a = 0
    (j[1]+1).times do |k|
      a += j[0]**k
    end
    arr[i] *= a

lune-sta

c, score = 0, 0
open("names.txt").gets.split(/,/).map{|a| a.delete("\"")}.sort.each do |i|
  c += 1
  i.size.times do |j|
    score += (i[j].bytes.to_a[0].to_i - "A".bytes.to_a[0].to_i + 1) * c
  end
end
puts score # 871198282

lune-sta

require 'prime'
m = 28123
sum = 0
adn = Array.new()
flag = Array.new(m+1){false}
2.upto(m) do |i|
  a = 1
  i.prime_division.each do |j|
    b = 0
    (j[1]+1).times do |k|

lune-sta

puts (0..9).to_a.permutation(10).to_a[1000000-1].join
# 2783915460

lune-sta

f = [1,1]
f.push(f[-1] + f[-2]) while f[-1].to_s.size < 1000
p f.size # 4782

lune-sta

require 'Prime'
max, answer = 0, 0
Prime.each(1000).to_a.reject{|p| p == 2 || p == 5}.each do |p|
  a, c = 10, 1
  while a % p != 1 do
    c += 1
    a *= 10
  end
  max, answer = c, p if max < c
end

lune-sta

require 'Prime'
max, answer = 0, 0
(-999..999).each do |a|
  Prime.each(999).to_a.each do |b|
    n = 0
    n += 1 while Prime.prime?(n ** 2 + a * n + b)
    max, answer = n, a * b if max < n
  end
end
puts answer # -59231