ZarankiewiczDB,

an online database of Zarankiewicz numbers.

z(15,20) = 75

By deleting 6 rows and 1 column from the finite projective plane of order 4.

lower bound = 75, submitted on April 22nd, 2016 (link)

By Roman's bound with $p = 3$. [Rom75]

upper bound = 75, submitted on April 22nd, 2016 (link)

Submit a result or comment?