991405440 has 128 divisors (see below), whose sum is σ = 3511288800. Its totient is φ = 264370176.

The previous prime is 991405433. The next prime is 991405469. The reversal of 991405440 is 44504199.

It is a happy number.

It is a tau number, because it is divible by the number of its divisors (128).

It is a Harshad number since it is a multiple of its sum of digits (36).

It is a junction number, because it is equal to n+sod(n) for n = 991405395 and 991405404.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 11407 + ... + 45966.

Almost surely, 2^991405440 is an apocalyptic number.

991405440 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 991405440, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1755644400).

991405440 is an abundant number, since it is smaller than the sum of its proper divisors (2519883360).

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

991405440 is a wasteful number, since it uses less digits than its factorization.

991405440 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 57401 (or 57383 counting only the distinct ones).

The product of its (nonzero) digits is 25920, while the sum is 36.

The square root of 991405440 is about 31486.5914319096. The cubic root of 991405440 is about 997.1268998678.

The spelling of 991405440 in words is "nine hundred ninety-one million, four hundred five thousand, four hundred forty".