18388621 has 2 divisors, whose sum is σ = 18388622. Its totient is φ = 18388620.

The previous prime is 18388583. The next prime is 18388631. The reversal of 18388621 is 12688381.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 17732521 + 656100 = 4211^2 + 810^2 .

It is a cyclic number.

It is not a de Polignac number, because 18388621 - 2⁷ = 18388493 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (18388631) 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 as a sum of consecutive naturals, namely, 9194310 + 9194311.

It is an arithmetic number, because the mean of its divisors is an integer number (9194311).

Almost surely, 2^18388621 is an apocalyptic number.

It is an amenable number.

18388621 is a deficient number, since it is larger than the sum of its proper divisors (1).

18388621 is an equidigital number, since it uses as much as digits as its factorization.

18388621 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 18432, while the sum is 37.

The square root of 18388621 is about 4288.1955412504. The cubic root of 18388621 is about 263.9467915801.

It can be divided in two parts, 183 and 88621, that added together give a square (88804 = 298²).

The spelling of 18388621 in words is "eighteen million, three hundred eighty-eight thousand, six hundred twenty-one".