Cutting a Hypertriangle

An $M$-dimensional hypertriangle is a regular $M$-dimensional polytope with $(M+1)$ vertices. For $M=2$ it is an equilateral triangle, and for $M=3$ it is a regular tetrahedron.

A block shaped like an $M$-dimensional hypertriangle with edge length $N$ is given. Cut the block parallel to each $(M-1)$-dimensional face so that every edge is divided into $N$ equal parts. Then select some of the pieces and combine them into an $M$-dimensional hypertriangle block without moving or rotating them from their original positions. The original block is solid, and the new block must also have no empty space inside. Write a program that counts the number of ways to form an $M$-dimensional hypertriangle block.

Two integers $M$ and $N$ are given, separated by a space. $(2\leq M,N\leq 100\,000)$

Print the number of ways to form an $M$-dimensional hypertriangle block. Since the number can be very large, print the remainder when divided by $10^{9}+7$. Note that $10^{9}+7$ is prime.

In this problem, two $(M-1)$-dimensional figures $a$ and $b$ in $M$-dimensional Euclidean space are called parallel when the following holds. Set an infinite $(M-1)$-dimensional space $A$ that contains $a$ and an infinite $(M-1)$-dimensional space $B$ that contains $b$. Every point of $A$ has the same distance to its orthogonal projection onto $B$, and that distance is not 0.