18638821 has 2 divisors, whose sum is σ = 18638822. Its totient is φ = 18638820.

The previous prime is 18638819. The next prime is 18638833. The reversal of 18638821 is 12883681.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 11826721 + 6812100 = 3439^2 + 2610^2 .

It is a cyclic number.

It is not a de Polignac number, because 18638821 - 2¹ = 18638819 is a prime.

Together with 18638819, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (18668821) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9319410 + 9319411.

It is an arithmetic number, because the mean of its divisors is an integer number (9319411).

Almost surely, 2^18638821 is an apocalyptic number.

It is an amenable number.

18638821 is a deficient number, since it is larger than the sum of its proper divisors (1).

18638821 is an equidigital number, since it uses as much as digits as its factorization.

18638821 is an evil number, because the sum of its binary digits is even.

The product of its digits is 18432, while the sum is 37.

The square root of 18638821 is about 4317.2700865246. The cubic root of 18638821 is about 265.1385107160.

The spelling of 18638821 in words is "eighteen million, six hundred thirty-eight thousand, eight hundred twenty-one".