Minecraft wiki entry for Explosion, associated text: Entities always get at least 1 point of damage if they are within the radius, regardless of their explosion exposure.
The maximum damage that entities can take (at the explosion center with 100% exposure and normal difficulty) = (1 × 1 + 1) × 7 × power + 1 point of damage = 99, (Wither newly spawned by the player), 85 (charged creepers), 71 (Beds when using in the Nether or in the End), 57 (TNT), 43 (creepers), 15 (fireballs). When entities are away or covered by blocks from the explosion center, they take less damage.
The maximum velocity gain that an entity can obtain from a single explosion is 1, at the explosion center with 100% exposure.