18387221 has 2 divisors, whose sum is σ = 18387222. Its totient is φ = 18387220.

The previous prime is 18387211. The next prime is 18387233. The reversal of 18387221 is 12278381.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 10491121 + 7896100 = 3239^2 + 2810^2 .

It is a cyclic number.

It is not a de Polignac number, because 18387221 - 2⁶ = 18387157 is a prime.

It is a super-2 number, since 2×18387221² = 676179792205682, which contains 22 as substring.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (18387211) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9193610 + 9193611.

It is an arithmetic number, because the mean of its divisors is an integer number (9193611).

Almost surely, 2^18387221 is an apocalyptic number.

It is an amenable number.

18387221 is a deficient number, since it is larger than the sum of its proper divisors (1).

18387221 is an equidigital number, since it uses as much as digits as its factorization.

18387221 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 5376, while the sum is 32.

The square root of 18387221 is about 4288.0322993187. The cubic root of 18387221 is about 263.9400929649.

The spelling of 18387221 in words is "eighteen million, three hundred eighty-seven thousand, two hundred twenty-one".