991721636 has 12 divisors (see below), whose sum is σ = 1810970112. Its totient is φ = 474301608.

The previous prime is 991721629. The next prime is 991721641. The reversal of 991721636 is 636127199.

991721636 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 5389700 + ... + 5389883.

It is an arithmetic number, because the mean of its divisors is an integer number (150914176).

Almost surely, 2^991721636 is an apocalyptic number.

It is an amenable number.

991721636 is a deficient number, since it is larger than the sum of its proper divisors (819248476).

991721636 is a wasteful number, since it uses less digits than its factorization.

991721636 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10779610 (or 10779608 counting only the distinct ones).

The product of its digits is 122472, while the sum is 44.

The square root of 991721636 is about 31491.6121530797. The cubic root of 991721636 is about 997.2328955286.

The spelling of 991721636 in words is "nine hundred ninety-one million, seven hundred twenty-one thousand, six hundred thirty-six".