result(n) = result(n-1)+4n-3+···
···时间不够了，后来想了想，如果n=2a,3b,4c...
1^n,2^n,...,(n-1)^n,n^n
(1^2)^a,
(2^2)^a,
...,
(x^2)^a,
(1^3)^b,
(2^3)^b,
...,
(y^3)^a,
(1^4)^a,
(2^4)^a,
...,
(z^4)^a,
...
只要算出x,y,z...
