18240021 has 6 divisors (see below), whose sum is σ = 26346710. Its totient is φ = 12160008.

The previous prime is 18240007. The next prime is 18240023. The reversal of 18240021 is 12004281.

It can be written as a sum of positive squares in only one way, i.e., 16892100 + 1347921 = 4110^2 + 1161^2 .

It is not a de Polignac number, because 18240021 - 2¹⁴ = 18223637 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 18239976 and 18240003.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (18240023) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 1013326 + ... + 1013343.

Almost surely, 2^18240021 is an apocalyptic number.

It is an amenable number.

18240021 is a deficient number, since it is larger than the sum of its proper divisors (8106689).

18240021 is a wasteful number, since it uses less digits than its factorization.

18240021 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2026675 (or 2026672 counting only the distinct ones).

The product of its (nonzero) digits is 128, while the sum is 18.

The square root of 18240021 is about 4270.8337593496. The cubic root of 18240021 is about 263.2338756314.

The spelling of 18240021 in words is "eighteen million, two hundred forty thousand, twenty-one".