18904021 has 2 divisors, whose sum is σ = 18904022. Its totient is φ = 18904020.

The previous prime is 18904019. The next prime is 18904033. The reversal of 18904021 is 12040981.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 17556100 + 1347921 = 4190^2 + 1161^2 .

It is a cyclic number.

It is not a de Polignac number, because 18904021 - 2¹ = 18904019 is a prime.

Together with 18904019, it forms a pair of twin primes.

It is equal to p_1205296 and since 18904021 and 1205296 have the same sum of digits, it is a Honaker prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (18904421) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9452010 + 9452011.

It is an arithmetic number, because the mean of its divisors is an integer number (9452011).

Almost surely, 2^18904021 is an apocalyptic number.

It is an amenable number.

18904021 is a deficient number, since it is larger than the sum of its proper divisors (1).

18904021 is an equidigital number, since it uses as much as digits as its factorization.

18904021 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 576, while the sum is 25.

The square root of 18904021 is about 4347.8754581979. The cubic root of 18904021 is about 266.3900894584.

The spelling of 18904021 in words is "eighteen million, nine hundred four thousand, twenty-one".