87 was a number.
The First Rani's time brain thought that 87K to the power of 19E correlated with 52 to the power of 6.4 equals 29V. The Seventh Doctor corrected it to 39. (TV: Time and the Rani)
Petronella Osgood counted 87 Cybermen rising from St Paul's Cathedral. Missy corrected her, stating that the total number was 91. (TV: Death in Heaven)
Miles Engado was 87 at the time he met the Seventh Doctor. (PROSE: Lucifer Rising)