991721883 has 4 divisors (see below), whose sum is σ = 1322295848. Its totient is φ = 661147920.

The previous prime is 991721869. The next prime is 991721893. The reversal of 991721883 is 388127199.

It is a semiprime because it is the product of two primes.

It is not a de Polignac number, because 991721883 - 2⁴ = 991721867 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (991721803) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 165286978 + ... + 165286983.

It is an arithmetic number, because the mean of its divisors is an integer number (330573962).

Almost surely, 2^991721883 is an apocalyptic number.

991721883 is a deficient number, since it is larger than the sum of its proper divisors (330573965).

991721883 is a wasteful number, since it uses less digits than its factorization.

991721883 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 330573964.

The product of its digits is 217728, while the sum is 48.

The square root of 991721883 is about 31491.6160747587. The cubic root of 991721883 is about 997.2329783195.

The spelling of 991721883 in words is "nine hundred ninety-one million, seven hundred twenty-one thousand, eight hundred eighty-three".