CF622F The Sum of the k-th Powers

There are well-known formulas: , , . Also mathematicians found similar formulas for higher degrees. Find the value of the sum  modulo $ 10^{9}+7 $ (so you should find the remainder after dividing the answer by the value $ 10^{9}+7 $ ).

The only line contains two integers $ n,k $ ( $ 1\le n\le10^{9},0\le k\le10^{6} $ ).

Print the only integer $ a $ — the remainder after dividing the value of the sum by the value $ 10^{9}+7 $ .