151011(4)

Ruby

Number of times 1 is used in writing out all the numbers 1 through n(3)

オンライン整数列大辞典のA014778のCOMMENTSを見ると、
このような性質をもつ数は84個あるらしい。
これらを出力してみる。

def A014778(n)
  i = 0
  cnt = 0
  ary = [0]
  num = 1
  while num < n
    i += 1
    cnt += i.to_s.count("1")
    if i == cnt
      ary << i
      num += 1
    end
  end
  ary
end

p A014778(84)

出力結果
[0, 1, 199981, 199982, 199983, 199984, 199985, 199986, 199987, 199988, 199989, 199990, 200000, 200001, 1599981, 1599982, 1599983, 1599984, 1599985, 1599986, 1599987, 1599988, 1599989, 1599990, 2600000, 2600001, 13199998, 35000000, 35000001, 35199981, 35199982, 35199983, 35199984, 35199985, 35199986, 35199987, 35199988, 35199989, 35199990, 35200000, 35200001, 117463825, 500000000, 500000001, 500199981, 500199982, 500199983, 500199984, 500199985, 500199986, 500199987, 500199988, 500199989, 500199990, 500200000, 500200001, 501599981, 501599982, 501599983, 501599984, 501599985, 501599986, 501599987, 501599988, 501599989, 501599990, 502600000, 502600001, 513199998, 535000000, 535000001, 535199981, 535199982, 535199983, 535199984, 535199985, 535199986, 535199987, 535199988, 535199989, 535199990, 535200000, 535200001, 1111111110]