18211720 has 32 divisors (see below), whose sum is σ = 41362200. Its totient is φ = 7216128.

The previous prime is 18211717. The next prime is 18211723. The reversal of 18211720 is 2711281.

It is an interprime number because it is at equal distance from previous prime (18211717) and next prime (18211723).

It can be written as a sum of positive squares in 4 ways, for example, as 17994564 + 217156 = 4242^2 + 466^2 .

It is a junction number, because it is equal to n+sod(n) for n = 18211691 and 18211700.

It is not an unprimeable number, because it can be changed into a prime (18211723) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 2272 + ... + 6448.

Almost surely, 2^18211720 is an apocalyptic number.

18211720 is a gapful number since it is divisible by the number (10) formed by its first and last digit.

It is an amenable number.

18211720 is an abundant number, since it is smaller than the sum of its proper divisors (23150480).

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

18211720 is a wasteful number, since it uses less digits than its factorization.

18211720 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4297 (or 4293 counting only the distinct ones).

The product of its (nonzero) digits is 224, while the sum is 22.

The square root of 18211720 is about 4267.5191856628. The cubic root of 18211720 is about 263.0976616391.

The spelling of 18211720 in words is "eighteen million, two hundred eleven thousand, seven hundred twenty".