同样方法，执行python 3.10a成功，注意必须重命名zip文件，否则报上述ModuleNotFoundError错误 D:\python310>python Python 3.10.0a4 (tags/v3.10.0a4:445f7f5, Jan 4 2021, 19:55:53) [MSC v.1928 64 bit (AMD64)] on win32 Type "help", "copyright", "credits" or "license" for more information.

缩进的空格被删除了 >>>> N=20 >>>> M=1000000007 >>>> s=[i for i in range(1,N+1)] >>>> s[1]=3 >>>> for i in range(2,N): .... s[i]=s[i-1]+s[i-2] .... if(s[i]>M): .... s[i]=s[i] % M .... >>>> for j in range(1,N-1): .... for i in range(j+1,N): .... s[i]+=s[i-1] .... if(s[i]>M): .... s[i]=s[i] % M .... >>>> print(s[N-1] % 1000000007) 742296999

@黄志斌 谢谢，所以n == 0是一个布尔值

http://oeis.org/A001499中的(PARI) a(n)=if(n<2, n==0, (n^2-n)*(a(n-1)+(n-1)/2*a(n-2)))怎么理解？

测试 N=20 M=1000000007 s=[i for i in range(1,N+1)] s[1]=3 for i in range(2,N): s[i]=s[i-1]+s[i-2] if(s[i]>M): s[i]=s[i] % M for j in range(1,N-1): for i in range(j+1,N): s[i]+=s[i-1] if(s[i]>M): s[i]=s[i] % M print(s[N-1] % 1000000007)