991997664 has 192 divisors, whose sum is σ = 3113510400. Its totient is φ = 270563328.

The previous prime is 991997627. The next prime is 991997681. The reversal of 991997664 is 466799199.

It is a junction number, because it is equal to n+sod(n) for n = 991997598 and 991997607.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 2123959 + ... + 2124425.

It is an arithmetic number, because the mean of its divisors is an integer number (16216200).

Almost surely, 2^991997664 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 991997664, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1556755200).

991997664 is an abundant number, since it is smaller than the sum of its proper divisors (2121512736).

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

991997664 is a wasteful number, since it uses less digits than its factorization.

991997664 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 625 (or 617 counting only the distinct ones).

The product of its digits is 6613488, while the sum is 60.

The square root of 991997664 is about 31495.9944119883. The cubic root of 991997664 is about 997.3254075997.

The spelling of 991997664 in words is "nine hundred ninety-one million, nine hundred ninety-seven thousand, six hundred sixty-four".