18440021 has 2 divisors, whose sum is σ = 18440022. Its totient is φ = 18440020.

The previous prime is 18440017. The next prime is 18440029. The reversal of 18440021 is 12004481.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 18369796 + 70225 = 4286^2 + 265^2 .

It is an emirp because it is prime and its reverse (12004481) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 18440021 - 2² = 18440017 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 18439975 and 18440002.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (18440029) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9220010 + 9220011.

It is an arithmetic number, because the mean of its divisors is an integer number (9220011).

Almost surely, 2^18440021 is an apocalyptic number.

It is an amenable number.

18440021 is a deficient number, since it is larger than the sum of its proper divisors (1).

18440021 is an equidigital number, since it uses as much as digits as its factorization.

18440021 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 256, while the sum is 20.

The square root of 18440021 is about 4294.1845558849. The cubic root of 18440021 is about 264.1924914243.

The spelling of 18440021 in words is "eighteen million, four hundred forty thousand, twenty-one".