991397940 has 72 divisors (see below), whose sum is σ = 3005902368. Its totient is φ = 244033920.

The previous prime is 991397923. The next prime is 991397947. The reversal of 991397940 is 49793199.

It is a Smith number, since the sum of its digits (51) coincides with the sum of the digits of its prime factors.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (991397947) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 38746 + ... + 59025.

It is an arithmetic number, because the mean of its divisors is an integer number (41748644).

Almost surely, 2^991397940 is an apocalyptic number.

It is an amenable number.

991397940 is an abundant number, since it is smaller than the sum of its proper divisors (2014504428).

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

991397940 is a wasteful number, since it uses less digits than its factorization.

991397940 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 97809 (or 97794 counting only the distinct ones).

The product of its (nonzero) digits is 551124, while the sum is 51.

The square root of 991397940 is about 31486.4723333688. The cubic root of 991397940 is about 997.1243854338.

The spelling of 991397940 in words is "nine hundred ninety-one million, three hundred ninety-seven thousand, nine hundred forty".