91721640 has 64 divisors (see below), whose sum is σ = 278510400. Its totient is φ = 24161792.

The previous prime is 91721629. The next prime is 91721657. The reversal of 91721640 is 4612719.

It is a happy number.

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

It is a junction number, because it is equal to n+sod(n) for n = 91721598 and 91721607.

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, 5356 + ... + 14564.

It is an arithmetic number, because the mean of its divisors is an integer number (4351725).

Almost surely, 2^91721640 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 91721640, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (139255200).

91721640 is an abundant number, since it is smaller than the sum of its proper divisors (186788760).

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

91721640 is a wasteful number, since it uses less digits than its factorization.

91721640 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 9306 (or 9302 counting only the distinct ones).

The product of its (nonzero) digits is 3024, while the sum is 30.

The square root of 91721640 is about 9577.1415359699. The cubic root of 91721640 is about 450.9799877387.

The spelling of 91721640 in words is "ninety-one million, seven hundred twenty-one thousand, six hundred forty".