18920821 has 2 divisors, whose sum is σ = 18920822. Its totient is φ = 18920820.

The previous prime is 18920809. The next prime is 18920831. The reversal of 18920821 is 12802981.

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., 17514225 + 1406596 = 4185^2 + 1186^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-18920821 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (18920831) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9460410 + 9460411.

It is an arithmetic number, because the mean of its divisors is an integer number (9460411).

Almost surely, 2^18920821 is an apocalyptic number.

It is an amenable number.

18920821 is a deficient number, since it is larger than the sum of its proper divisors (1).

18920821 is an equidigital number, since it uses as much as digits as its factorization.

18920821 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 2304, while the sum is 31.

The square root of 18920821 is about 4349.8070072131. The cubic root of 18920821 is about 266.4689797010.

The spelling of 18920821 in words is "eighteen million, nine hundred twenty thousand, eight hundred twenty-one".