Terms of the deals were not disclosed by the Wizards, who also acquired guard Trey Burke from Utah for a 2021 second-round pick. The ninth overall pick of the 2013 draft, Burke has averaged 12.1 points, 4.2 assists and 2.5 rebounds in three seasons with Utah and is expected to back up All-Star guard John Wall.
Mahinmi recorded career-highs in points (9.3) and rebounds (7.1) last season with Indiana. Those numbers were considerably better than the 5.1 points and 4.3 rebounds he averaged in his previous eight campaigns with San Antonio, Dallas and the Pacers.
"Ian will give us defense, rebounding and rim protection at the backup center position," Washington president Ernie Grunfeld said. "He is a physical, experienced player who proved himself last season as a starter and will provide great depth for our frontcourt."
Nicholson averaged 6.9 points and 3.2 rebounds last season with Orlando. The 19th overall pick of the 2012 draft, Nicholson has shot 33.6 percent from 3-point range in 247 career contests.
"Andrew is a very intriguing young talent who has shown the ability to score from both inside and outside as he has developed throughout his career," Grunfeld said. "His skill set will help bolster our frontcourt depth and we feel he has good potential to continue to improve."
Smith has averaged 6.5 points and 3.5 rebounds over nine seasons with Philadelphia, New Orleans, New York and Orlando. The journeyman stepped it up in 2015-16, averaging 7.2 points in 76 games.