1991821524 has 144 divisors (see below), whose sum is σ = 6156111360. Its totient is φ = 486858240.

The previous prime is 1991821523. The next prime is 1991821537. The reversal of 1991821524 is 4251281991.

1991821524 is digitally balanced in base 4, because in such base it contains all the possibile digits an equal number of times.

It is a Harshad number since it is a multiple of its sum of digits (42).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1991821523) 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, 263307 + ... + 270765.

Almost surely, 2^1991821524 is an apocalyptic number.

1991821524 is a gapful number since it is divisible by the number (14) 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 1991821524, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (3078055680).

1991821524 is an abundant number, since it is smaller than the sum of its proper divisors (4164289836).

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

1991821524 is a wasteful number, since it uses less digits than its factorization.

1991821524 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7518 (or 7499 counting only the distinct ones).

The product of its digits is 51840, while the sum is 42.

The square root of 1991821524 is about 44629.8277388564. The cubic root of 1991821524 is about 1258.2013313027.

The spelling of 1991821524 in words is "one billion, nine hundred ninety-one million, eight hundred twenty-one thousand, five hundred twenty-four".