91009920 has 128 divisors (see below), whose sum is σ = 293466240. Its totient is φ = 23988224.

The previous prime is 91009913. The next prime is 91009931. The reversal of 91009920 is 2990019.

It is a tau number, because it is divible by the number of its divisors (128).

It is a Harshad number since it is a multiple of its sum of digits (30).

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 205219 + ... + 205661.

It is an arithmetic number, because the mean of its divisors is an integer number (2292705).

Almost surely, 2^91009920 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 91009920, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (146733120).

91009920 is an abundant number, since it is smaller than the sum of its proper divisors (202456320).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

91009920 is a wasteful number, since it uses less digits than its factorization.

91009920 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 572 (or 560 counting only the distinct ones).

The product of its (nonzero) digits is 1458, while the sum is 30.

The square root of 91009920 is about 9539.9119492792. The cubic root of 91009920 is about 449.8104881019.

Adding to 91009920 its reverse (2990019), we get a palindrome (93999939).

The spelling of 91009920 in words is "ninety-one million, nine thousand, nine hundred twenty".