--description--

Consider the number 45656.

It can be seen that each pair of consecutive digits of 45656 has a difference of one.

A number for which every pair of consecutive digits has a difference of one is called a step number.

A pandigital number contains every decimal digit from 0 to 9 at least once.

How many pandigital step numbers less than ${10}^{40}$ are there?

--hints--

stepNumbers() should return 126461847755.

assert.strictEqual(stepNumbers(), 126461847755);

--seed--

--seed-contents--

function stepNumbers() {

  return true;
}

stepNumbers();

--solutions--

// solution required