18687721382021 has 4 divisors (see below), whose sum is σ = 18689509177932. Its totient is φ = 18685933586112.

The previous prime is 18687721382017. The next prime is 18687721382117. The reversal of 18687721382021 is 12028312778681.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 11583737373121 + 7103984008900 = 3403489^2 + 2665330^2 .

It is a cyclic number.

It is not a de Polignac number, because 18687721382021 - 2² = 18687721382017 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 (18687721352021) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (23) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 893882276 + ... + 893903181.

It is an arithmetic number, because the mean of its divisors is an integer number (4672377294483).

Almost surely, 2^{18687721382021} is an apocalyptic number.

It is an amenable number.

18687721382021 is a deficient number, since it is larger than the sum of its proper divisors (1787795911).

18687721382021 is a wasteful number, since it uses less digits than its factorization.

18687721382021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1787795910.

The product of its (nonzero) digits is 3612672, while the sum is 56.

The spelling of 18687721382021 in words is "eighteen trillion, six hundred eighty-seven billion, seven hundred twenty-one million, three hundred eighty-two thousand, twenty-one".