991788840 has 256 divisors, whose sum is σ = 4001011200. Its totient is φ = 213331968.

The previous prime is 991788839. The next prime is 991788869. The reversal of 991788840 is 48887199.

It is a super-3 number, since 3×991788840³ (a number of 28 digits) contains 333 as substring.

It is a Harshad number since it is a multiple of its sum of digits (54).

It is an unprimeable number.

It is a polite number, since it can be written in 63 ways as a sum of consecutive naturals, for example, 124662 + ... + 132378.

It is an arithmetic number, because the mean of its divisors is an integer number (15628950).

Almost surely, 2^991788840 is an apocalyptic number.

991788840 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 991788840, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (2000505600).

991788840 is an abundant number, since it is smaller than the sum of its proper divisors (3009222360).

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

991788840 is a wasteful number, since it uses less digits than its factorization.

991788840 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7761 (or 7751 counting only the distinct ones).

The product of its (nonzero) digits is 1161216, while the sum is 54.

The square root of 991788840 is about 31492.6791492880. The cubic root of 991788840 is about 997.2554208433.

The spelling of 991788840 in words is "nine hundred ninety-one million, seven hundred eighty-eight thousand, eight hundred forty".