31578189906821 has 4 divisors (see below), whose sum is σ = 31579045419852. Its totient is φ = 31577334393792.

The previous prime is 31578189906751. The next prime is 31578189906833. The reversal of 31578189906821 is 12860998187513.

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 30623053116100 + 955136790721 = 5533810^2 + 977311^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-31578189906821 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (31578189909821) 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, 427701146 + ... + 427774971.

It is an arithmetic number, because the mean of its divisors is an integer number (7894761354963).

Almost surely, 2^{31578189906821} is an apocalyptic number.

It is an amenable number.

31578189906821 is a deficient number, since it is larger than the sum of its proper divisors (855513031).

31578189906821 is an equidigital number, since it uses as much as digits as its factorization.

31578189906821 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 855513030.

The product of its (nonzero) digits is 52254720, while the sum is 68.

The spelling of 31578189906821 in words is "thirty-one trillion, five hundred seventy-eight billion, one hundred eighty-nine million, nine hundred six thousand, eight hundred twenty-one".