991638000 has 240 divisors, whose sum is σ = 3508034400. Its totient is φ = 261043200.

The previous prime is 991637953. The next prime is 991638001. The reversal of 991638000 is 836199.

It is a tau number, because it is divible by the number of its divisors (240).

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

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (991638001) by changing a digit.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 1601691 + ... + 1602309.

It is an arithmetic number, because the mean of its divisors is an integer number (14616810).

Almost surely, 2^991638000 is an apocalyptic number.

991638000 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 991638000, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1754017200).

991638000 is an abundant number, since it is smaller than the sum of its proper divisors (2516396400).

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

991638000 is a wasteful number, since it uses less digits than its factorization.

991638000 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 737 (or 718 counting only the distinct ones).

The product of its (nonzero) digits is 11664, while the sum is 36.

The square root of 991638000 is about 31490.2842159292. The cubic root of 991638000 is about 997.2048611447.

The spelling of 991638000 in words is "nine hundred ninety-one million, six hundred thirty-eight thousand".