18781021 has 4 divisors (see below), whose sum is σ = 21464032. Its totient is φ = 16098012.

The previous prime is 18781013. The next prime is 18781033. The reversal of 18781021 is 12018781.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is not a de Polignac number, because 18781021 - 2³ = 18781013 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (18781001) 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, 1341495 + ... + 1341508.

It is an arithmetic number, because the mean of its divisors is an integer number (5366008).

Almost surely, 2^18781021 is an apocalyptic number.

It is an amenable number.

18781021 is a deficient number, since it is larger than the sum of its proper divisors (2683011).

18781021 is an equidigital number, since it uses as much as digits as its factorization.

18781021 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2683010.

The product of its (nonzero) digits is 896, while the sum is 28.

The square root of 18781021 is about 4333.7075351251. The cubic root of 18781021 is about 265.8110714896.

The spelling of 18781021 in words is "eighteen million, seven hundred eighty-one thousand, twenty-one".