1991243280 has 320 divisors, whose sum is σ = 6884559360. Its totient is φ = 473088000.

The previous prime is 1991243273. The next prime is 1991243281. The reversal of 1991243280 is 823421991.

It is a Harshad number since it is a multiple of its sum of digits (39).

It is not an unprimeable number, because it can be changed into a prime (1991243281) by changing a digit.

It is a polite number, since it can be written in 63 ways as a sum of consecutive naturals, for example, 19715230 + ... + 19715330.

It is an arithmetic number, because the mean of its divisors is an integer number (21514248).

Almost surely, 2^1991243280 is an apocalyptic number.

1991243280 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 1991243280, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (3442279680).

1991243280 is an abundant number, since it is smaller than the sum of its proper divisors (4893316080).

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

1991243280 is a wasteful number, since it uses less digits than its factorization.

1991243280 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 290 (or 284 counting only the distinct ones).

The product of its (nonzero) digits is 31104, while the sum is 39.

The square root of 1991243280 is about 44623.3490450907. The cubic root of 1991243280 is about 1258.0795637351.

The spelling of 1991243280 in words is "one billion, nine hundred ninety-one million, two hundred forty-three thousand, two hundred eighty".