18521821 has 2 divisors, whose sum is σ = 18521822. Its totient is φ = 18521820.

The previous prime is 18521813. The next prime is 18521837. The reversal of 18521821 is 12812581.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 10169721 + 8352100 = 3189^2 + 2890^2 .

It is a cyclic number.

It is not a de Polignac number, because 18521821 - 2³ = 18521813 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 18521821.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (18521801) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9260910 + 9260911.

It is an arithmetic number, because the mean of its divisors is an integer number (9260911).

Almost surely, 2^18521821 is an apocalyptic number.

It is an amenable number.

18521821 is a deficient number, since it is larger than the sum of its proper divisors (1).

18521821 is an equidigital number, since it uses as much as digits as its factorization.

18521821 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 1280, while the sum is 28.

The square root of 18521821 is about 4303.6985256869. The cubic root of 18521821 is about 264.5825681476.

The spelling of 18521821 in words is "eighteen million, five hundred twenty-one thousand, eight hundred twenty-one".