def _n3(n, a, b, x):
    """Recurrence coefficients for n-1, n, n+11 (a, b all equal).
    """
    return {(n - 1, a, b): +2 * (n + a) * (n + b) * (2 * n + a + b + 2), (n,
        a, b): -(2 * n + a + b + 1) * (a ** 2 - b ** 2 + x * (2 * n + a + b
        ) * (2 * n + a + b + 2)), (n + 1, a, b): +2 * (n + 1) * (n + a + b +
        1) * (2 * n + a + b)}
