• 85 can be written using four 4's:
85 is nontrivially palindromic in base 2, base 4, base 7 and base 16.
85 is an esthetic number in base 2, base 11 and base 13, because in such bases its adjacent digits differ by 1.
It is a 3-Lehmer number, since φ(85) divides (85-1)3.
It is a cyclic number.
85 is an idoneal number.
It is the 8-th Jacobsthal number.
It is a magnanimous number.
It is an alternating number because its digits alternate between even and odd.
It is a Duffinian number.
85 is an undulating number in base 2 and base 7.
85 is a nontrivial repdigit in base 4 and base 16.
It is a plaindrome in base 4, base 8, base 11, base 13, base 15 and base 16.
It is a nialpdrome in base 4, base 5, base 6, base 10, base 12, base 14 and base 16.
It is a zygodrome in base 4 and base 16.
It is a congruent number.
It is a panconsummate number.
In principle, a polygon with 85 sides can be constructed with ruler and compass.
85 is the 5-th decagonal number.
It is an amenable number.
85 is a wasteful number, since it uses less digits than its factorization.
85 is an evil number, because the sum of its binary digits is even.
The sum of its prime factors is 22.
The square root of 85 is about 9.2195444573. The cubic root of 85 is about 4.3968296722.
Adding to 85 its product of digits (40), we get a cube (125 = 53).
Subtracting from 85 its product of digits (40), we obtain a triangular number (45 = T9).
Subtracting from 85 its reverse (58), we obtain a cube (27 = 33).