## Admissible paths through a grid

### Problem 408

Let's call a lattice point (`x`, `y`) *inadmissible* if `x`, `y` and `x` + `y` are all positive perfect squares.

For example, (9, 16) is inadmissible, while (0, 4), (3, 1) and (9, 4) are not.

Consider a path from point (`x`_{1}, `y`_{1}) to point (`x`_{2}, `y`_{2}) using only unit steps north or east.

Let's call such a path *admissible* if none of its intermediate points are inadmissible.

Let P(`n`) be the number of admissible paths from (0, 0) to (`n`, `n`).

It can be verified that P(5) = 252, P(16) = 596994440 and P(1000) mod 1 000 000 007 = 341920854.

Find P(10 000 000) mod 1 000 000 007.