The Titius–Bode law is a hypothesis that the bodies in some orbital systems, including the Sun

Sun

The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...

's, orbit at semi-major axes

Semi-major axis

The major axis of an ellipse is its longest diameter, a line that runs through the centre and both foci, its ends being at the widest points of the shape...

 in a function of planetary sequence. The hypothesis correctly predicted the orbits of Ceres and Uranus

Uranus

Uranus is the seventh planet from the Sun. It has the third-largest planetary radius and fourth-largest planetary mass in the Solar System. It is named after the ancient Greek deity of the sky Uranus , the father of Cronus and grandfather of Zeus...

, but failed as a predictor of Neptune

Neptune

Neptune is the eighth and farthest planet from the Sun in the Solar System. Named for the Roman god of the sea, it is the fourth-largest planet by diameter and the third largest by mass. Neptune is 17 times the mass of Earth and is slightly more massive than its near-twin Uranus, which is 15 times...

's orbit.
The law relates the semi-major axis of each planet outward from the Sun in units such that the Earth's semi-major axis is equal to 10:

a = 4 + n

where n = 0, 3, 6, 12, 24, 48 …, each value of n > 3 twice the previous value.