a[n+1] + (n+1)a[n] = b[n]
b[n+1] + (n+1)b[n] = 0
a[1] = 1, b[1] = -1
のときのa[n], b[n]の一般項を
h[n] = 農[k=1,n](1/k)
を用いて求めよ。