151011(5)

Ruby

Number of times 1 is used in writing out all the numbers 1 through n(4)

オンライン整数列大辞典の
A094798（http://oeis.org/A094798/list）
と比較し、答え合わせしてみる。

def A094798(n)
  i = 0
  cnt = 0
  ary = []
  while i < n
    i += 1
    cnt += i.to_s.count("1")
    ary << cnt
  end
  ary
end
ary = A094798(75)

# OEIS A094798のデータ
ary0 =
[1,1,1,1,1,1,1,1,1,2,4,5,6,7,8,9,10,11,12,12,13,
 13,13,13,13,13,13,13,13,13,14,14,14,14,14,14,14,
 14,14,14,15,15,15,15,15,15,15,15,15,15,16,16,16,
 16,16,16,16,16,16,16,17,17,17,17,17,17,17,17,17,
 17,18,18,18,18,18]
# 一致の確認
p ary == ary0