18257221 has 4 divisors (see below), whose sum is σ = 18352012. Its totient is φ = 18162432.

The previous prime is 18257207. The next prime is 18257249. The reversal of 18257221 is 12275281.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 12275281 = 521 ⋅23561.

It can be written as a sum of positive squares in 2 ways, for example, as 11937025 + 6320196 = 3455^2 + 2514^2 .

It is a cyclic number.

It is not a de Polignac number, because 18257221 - 2⁷ = 18257093 is a prime.

It is a super-4 number, since 4×18257221⁴ (a number of 30 digits) contains 4444 as substring. Note that it is a super-d number also for d = 2.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 18257221.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (18257251) 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 3 ways as a sum of consecutive naturals, for example, 47106 + ... + 47491.

It is an arithmetic number, because the mean of its divisors is an integer number (4588003).

Almost surely, 2^18257221 is an apocalyptic number.

It is an amenable number.

18257221 is a deficient number, since it is larger than the sum of its proper divisors (94791).

18257221 is an equidigital number, since it uses as much as digits as its factorization.

18257221 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 94790.

The product of its digits is 2240, while the sum is 28.

The square root of 18257221 is about 4272.8469431984. The cubic root of 18257221 is about 263.3165911840.

The spelling of 18257221 in words is "eighteen million, two hundred fifty-seven thousand, two hundred twenty-one".