151210(2)

Ruby


Number of partitions of n that do not contain 1 as a part(1)

オンライン整数列大辞典の
A002865（http://oeis.org/A002865/list）
と比較し、答え合わせしてみる。

def A002865(n)
  ps = Array.new(n + 1){0}
  ps[0] = 1
  (2..n).each{|num|
    (num..n).each{|i|
      ps[i] += ps[i - num]
    }
  }
  ps
end
ary = A002865(50)

# OEIS A002865のデータ
ary0 =
[1,0,1,1,2,2,4,4,7,8,12,14,21,24,34,41,55,66,88,
 105,137,165,210,253,320,383,478,574,708,847,1039,
 1238,1507,1794,2167,2573,3094,3660,4378,5170,6153,
 7245,8591,10087,11914,13959,16424,19196,22519,
 26252,30701]
# 一致の確認
p ary == ary0