991972638 has 12 divisors (see below), whose sum is σ = 2149274088. Its totient is φ = 330657540.

The previous prime is 991972609. The next prime is 991972669. The reversal of 991972638 is 836279199.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 27554778 + ... + 27554813.

It is an arithmetic number, because the mean of its divisors is an integer number (179106174).

Almost surely, 2^991972638 is an apocalyptic number.

991972638 is an abundant number, since it is smaller than the sum of its proper divisors (1157301450).

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

991972638 is a wasteful number, since it uses less digits than its factorization.

991972638 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 55109599 (or 55109596 counting only the distinct ones).

The product of its digits is 1469664, while the sum is 54.

The square root of 991972638 is about 31495.5971208675. The cubic root of 991972638 is about 997.3170207266.

The spelling of 991972638 in words is "nine hundred ninety-one million, nine hundred seventy-two thousand, six hundred thirty-eight".