91809 has 9 divisors (see below), whose sum is σ = 133939.
Its totient is φ = 60600.
The previous prime is 91807. The next prime is 91811. The reversal of 91809 is 90819.
91809 = T302 + T303.
The square root of 91809 is 303.
It is a perfect power (a square), and thus also a powerful number.
It is an interprime number because it is at equal distance from previous prime (91807) and next prime (91811).
It can be written as a sum of positive squares in only one way, i.e., 88209 + 3600 = 297^2 + 60^2
It is a tau number, because it is divible by the number of its divisors (9).
It is not a de Polignac number, because 91809 - 21 = 91807 is a prime.
It is a Duffinian number.
It is a zygodrome in base 3.
It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 91809.
It is not an unprimeable number, because it can be changed into a prime (91801) by changing a digit.
It is a polite number, since it can be written in 8 ways as a sum of consecutive naturals, for example, 859 + ... + 959.
291809 is an apocalyptic number.
91809 is the 303-rd square number.
91809 is the 152-nd centered octagonal number.
It is an amenable number.
91809 is a deficient number, since it is larger than the sum of its proper divisors (42130).
91809 is a wasteful number, since it uses less digits than its factorization.
91809 is an evil number, because the sum of its binary digits is even.
The sum of its prime factors is 208 (or 104 counting only the distinct ones).
The product of its (nonzero) digits is 648, while the sum is 27.
The cubic root of 91809 is about 45.1123120484.
Subtracting from 91809 its reverse (90819), we obtain a triangular number (990 = T44).
It can be divided in two parts, 91 and 809, that added together give a square (900 = 302).
The spelling of 91809 in words is "ninety-one thousand, eight hundred nine".