991040778 has 192 divisors, whose sum is σ = 2822238720. Its totient is φ = 255394944.

The previous prime is 991040761. The next prime is 991040801. The reversal of 991040778 is 877040199.

It is an unprimeable number.

It is a polite number, since it can be written in 95 ways as a sum of consecutive naturals, for example, 1616400 + ... + 1617012.

It is an arithmetic number, because the mean of its divisors is an integer number (14699160).

Almost surely, 2^991040778 is an apocalyptic number.

991040778 is a gapful number since it is divisible by the number (98) formed by its first and last digit.

It is a practical number, because each smaller number is the sum of distinct divisors of 991040778, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1411119360).

991040778 is an abundant number, since it is smaller than the sum of its proper divisors (1831197942).

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

991040778 is a wasteful number, since it uses less digits than its factorization.

991040778 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 698 (or 685 counting only the distinct ones).

The product of its (nonzero) digits is 127008, while the sum is 45.

The square root of 991040778 is about 31480.8001486620. The cubic root of 991040778 is about 997.0046293799.

The spelling of 991040778 in words is "nine hundred ninety-one million, forty thousand, seven hundred seventy-eight".