A page of the Numeropedia - the Special Encyclopedia of Numbers
[Language] Nonagenarian is a person whose age is 90 to 99 years old.
[Sport] The jersey numbers most usually worn by American football players in the linebackers and defensive line (defensive ends, defensive tackles and nose guard)positions.
90--91 (and 87, 88 & 89)
[Tech.] Octane (R+M)/2 antiknock index rating of unleaded gasoline for automobiles in the U.S.: 87, 88, 89, 90 and 91.
[Library] Numbers 000-099 are the first 3 digits in Dewey Decimal Classification System call numbers for library books in Generalities (Bibliographies, Encyclopedias, Magazines and Computer Science…). Numbers 090-099 are for books in Manuscripts and Rare Books.
91-99 & 991-999 & 9991-9999 & 99991-99999…
[Math.] Repeatedly inserting number 9 before ab and number 0 before cdin the square number abcd = (9x)2yields the square numbers: (99x)2 = 9ab0cd; (999x)2 = 99ab00cd…, for x = 1 to 9.
The numbers commonly assigned for lower level undergraduate (the first 2 college years, freshman and sophomore) courses in most U.S. universities and colleges.