991259640 has 512 divisors, whose sum is σ = 4073472000. Its totient is φ = 209392128.

The previous prime is 991259639. The next prime is 991259683. The reversal of 991259640 is 46952199.

991259640 is a `hidden beast` number, since 9 + 9 + 12 + 596 + 40 = 666.

It is a Harshad number since it is a multiple of its sum of digits (45).

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 127 ways as a sum of consecutive naturals, for example, 9623829 + ... + 9623931.

It is an arithmetic number, because the mean of its divisors is an integer number (7956000).

Almost surely, 2^991259640 is an apocalyptic number.

991259640 is a gapful number since it is divisible by the number (90) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 991259640, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (2036736000).

991259640 is an abundant number, since it is smaller than the sum of its proper divisors (3082212360).

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

991259640 is a wasteful number, since it uses less digits than its factorization.

991259640 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 216 (or 206 counting only the distinct ones).

The product of its (nonzero) digits is 174960, while the sum is 45.

The square root of 991259640 is about 31484.2760755270. The cubic root of 991259640 is about 997.0780169980.

The spelling of 991259640 in words is "nine hundred ninety-one million, two hundred fifty-nine thousand, six hundred forty".