Douglas Harper's Etymology Dictionary
sesquicentennial
"pertaining to a century and a half," 1878, from sesqui- + centennial. As a noun from 1880; first recorded reference is to Baltimore's.
Wiktionary
sesquicentennial
a. 1 Occurring every 150 years 2 Of, or relating to a sesquicentenary n. A 150th anniversary.
Usage examples of "sesquicentennial".
It boded well for the sesquicentennial celebration of Pickax City, 400 miles north of everywhere.