尾递归解决类斐波那契数列
牛牛学数列6
https://www.nowcoder.com/practice/b6321648517247b2ac2e2f80cbc63ae1
n = int(input())
def A(i,a,b,c):
if i ==1:
return(a)
elif i == 2:
return(b)
elif i == 3:
return(c)
else:
return A(i-1,b,c,a+2*b+c)
S = A(n,0,1,1)
print(S)
