18521021 has 2 divisors, whose sum is σ = 18521022. Its totient is φ = 18521020.

The previous prime is 18520993. The next prime is 18521023. The reversal of 18521021 is 12012581.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 16728100 + 1792921 = 4090^2 + 1339^2 .

It is a cyclic number.

It is not a de Polignac number, because 18521021 - 2¹⁰ = 18519997 is a prime.

Together with 18521023, it forms a pair of twin primes.

It is a Chen prime.

It is a junction number, because it is equal to n+sod(n) for n = 18520984 and 18521002.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (18521023) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9260510 + 9260511.

It is an arithmetic number, because the mean of its divisors is an integer number (9260511).

Almost surely, 2^18521021 is an apocalyptic number.

It is an amenable number.

18521021 is a deficient number, since it is larger than the sum of its proper divisors (1).

18521021 is an equidigital number, since it uses as much as digits as its factorization.

18521021 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 160, while the sum is 20.

The square root of 18521021 is about 4303.6055813701. The cubic root of 18521021 is about 264.5787587831.

The spelling of 18521021 in words is "eighteen million, five hundred twenty-one thousand, twenty-one".