18221312 has 36 divisors (see below), whose sum is σ = 36761340. Its totient is φ = 9013248.

The previous prime is 18221257. The next prime is 18221339. The reversal of 18221312 is 21312281.

It can be written as a sum of positive squares in 2 ways, for example, as 8386816 + 9834496 = 2896^2 + 3136^2 .

It is a super-2 number, since 2×18221312² = 664032422002688, which contains 22 as substring.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 27578 + ... + 28230.

Almost surely, 2^18221312 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 18221312, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (18380670).

18221312 is an abundant number, since it is smaller than the sum of its proper divisors (18540028).

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

18221312 is an equidigital number, since it uses as much as digits as its factorization.

18221312 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 778 (or 764 counting only the distinct ones).

The product of its digits is 192, while the sum is 20.

The square root of 18221312 is about 4268.6428756690. The cubic root of 18221312 is about 263.1438441677.

Adding to 18221312 its reverse (21312281), we get a palindrome (39533593).

The spelling of 18221312 in words is "eighteen million, two hundred twenty-one thousand, three hundred twelve".