1991329920 has 320 divisors, whose sum is σ = 7197854400. Its totient is φ = 524593152.

The previous prime is 1991329891. The next prime is 1991329987. The reversal of 1991329920 is 299231991.

It is a tau number, because it is divible by the number of its divisors (320).

It is a Harshad number since it is a multiple of its sum of digits (45).

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 39 ways as a sum of consecutive naturals, for example, 5546701 + ... + 5547059.

It is an arithmetic number, because the mean of its divisors is an integer number (22493295).

Almost surely, 2^1991329920 is an apocalyptic number.

1991329920 is a gapful number since it is divisible by the number (10) 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 1991329920, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (3598927200).

1991329920 is an abundant number, since it is smaller than the sum of its proper divisors (5206524480).

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

1991329920 is a wasteful number, since it uses less digits than its factorization.

1991329920 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 497 (or 476 counting only the distinct ones).

The product of its (nonzero) digits is 78732, while the sum is 45.

The square root of 1991329920 is about 44624.3198267492. The cubic root of 1991329920 is about 1258.0978100294.

The spelling of 1991329920 in words is "one billion, nine hundred ninety-one million, three hundred twenty-nine thousand, nine hundred twenty".