18217021 has 2 divisors, whose sum is σ = 18217022. Its totient is φ = 18217020.

The previous prime is 18217019. The next prime is 18217037. The reversal of 18217021 is 12071281.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 12880921 + 5336100 = 3589^2 + 2310^2 .

It is an emirp because it is prime and its reverse (12071281) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 18217021 - 2¹ = 18217019 is a prime.

It is a super-2 number, since 2×18217021² = 663719708228882, which contains 22 as substring.

Together with 18217019, it forms a pair of twin primes.

It is a junction number, because it is equal to n+sod(n) for n = 18216983 and 18217001.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (18217051) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9108510 + 9108511.

It is an arithmetic number, because the mean of its divisors is an integer number (9108511).

Almost surely, 2^18217021 is an apocalyptic number.

It is an amenable number.

18217021 is a deficient number, since it is larger than the sum of its proper divisors (1).

18217021 is an equidigital number, since it uses as much as digits as its factorization.

18217021 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 224, while the sum is 22.

The square root of 18217021 is about 4268.1402273121. The cubic root of 18217021 is about 263.1231863270.

The spelling of 18217021 in words is "eighteen million, two hundred seventeen thousand, twenty-one".