1821397720 has 16 divisors (see below), whose sum is σ = 4098144960. Its totient is φ = 728559072.

The previous prime is 1821397709. The next prime is 1821397723. The reversal of 1821397720 is 277931281.

It is a happy number.

It is a Harshad number since it is a multiple of its sum of digits (40), and also a Moran number because the ratio is a prime number: 45534943 = 1821397720 / (1 + 8 + 2 + 1 + 3 + 9 + 7 + 7 + 2 + 0).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1821397723) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 22767432 + ... + 22767511.

It is an arithmetic number, because the mean of its divisors is an integer number (256134060).

Almost surely, 2^1821397720 is an apocalyptic number.

1821397720 is a gapful number since it is divisible by the number (10) formed by its first and last digit.

It is an amenable number.

1821397720 is an abundant number, since it is smaller than the sum of its proper divisors (2276747240).

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

1821397720 is a wasteful number, since it uses less digits than its factorization.

1821397720 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 45534954 (or 45534950 counting only the distinct ones).

The product of its (nonzero) digits is 42336, while the sum is 40.

The square root of 1821397720 is about 42677.8364025169. The cubic root of 1821397720 is about 1221.2416186885.

The spelling of 1821397720 in words is "one billion, eight hundred twenty-one million, three hundred ninety-seven thousand, seven hundred twenty".