991721664 has 112 divisors (see below), whose sum is σ = 2939084800. Its totient is φ = 327898368.

The previous prime is 991721641. The next prime is 991721669. The reversal of 991721664 is 466127199.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (991721669) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 217197 + ... + 221715.

Almost surely, 2^991721664 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 991721664, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1469542400).

991721664 is an abundant number, since it is smaller than the sum of its proper divisors (1947363136).

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

991721664 is a wasteful number, since it uses less digits than its factorization.

991721664 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4667 (or 4651 counting only the distinct ones).

The product of its digits is 163296, while the sum is 45.

The square root of 991721664 is about 31491.6125976426. The cubic root of 991721664 is about 997.2329049138.

The spelling of 991721664 in words is "nine hundred ninety-one million, seven hundred twenty-one thousand, six hundred sixty-four".