18863821 has 4 divisors (see below), whose sum is σ = 19373692. Its totient is φ = 18353952.

The previous prime is 18863809. The next prime is 18863839. The reversal of 18863821 is 12836881.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 12836881 = 2203 ⋅5827.

It can be written as a sum of positive squares in 2 ways, for example, as 15888196 + 2975625 = 3986^2 + 1725^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-18863821 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (37), and also a Moran number because the ratio is a prime number: 509833 = 18863821 / (1 + 8 + 8 + 6 + 3 + 8 + 2 + 1).

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (18863521) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 254880 + ... + 254953.

It is an arithmetic number, because the mean of its divisors is an integer number (4843423).

Almost surely, 2^18863821 is an apocalyptic number.

It is an amenable number.

18863821 is a deficient number, since it is larger than the sum of its proper divisors (509871).

18863821 is an equidigital number, since it uses as much as digits as its factorization.

18863821 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 509870.

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

The square root of 18863821 is about 4343.2500503655. The cubic root of 18863821 is about 266.2011264594.

It can be divided in two parts, 188 and 63821, that added together give a square (64009 = 253²).

The spelling of 18863821 in words is "eighteen million, eight hundred sixty-three thousand, eight hundred twenty-one".