def polyderiv(a):
	"""
	p'(x) = polyderiv(a)
	      = b[0] + b[1]x + b[2]x^2 +...+ b[n-2]x^{n-2} + b[n-1]x^{n-1}
	where b[i] = (i+1)a[i+1]
	"""
	b = []
	for i in range(1, len(a)):
		b.append(i * a[i])
	return b