21235120685 has 4 divisors (see below), whose sum is σ = 25482144828. Its totient is φ = 16988096544.

The previous prime is 21235120667. The next prime is 21235120721. The reversal of 21235120685 is 58602153212.

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 7925806729 + 13309313956 = 89027^2 + 115366^2 .

It is a cyclic number.

It is not a de Polignac number, because 21235120685 - 2⁸ = 21235120429 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2123512064 + ... + 2123512073.

It is an arithmetic number, because the mean of its divisors is an integer number (6370536207).

Almost surely, 2^21235120685 is an apocalyptic number.

It is an amenable number.

21235120685 is a deficient number, since it is larger than the sum of its proper divisors (4247024143).

21235120685 is an equidigital number, since it uses as much as digits as its factorization.

21235120685 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4247024142.

The product of its (nonzero) digits is 28800, while the sum is 35.

Adding to 21235120685 its reverse (58602153212), we get a palindrome (79837273897).

The spelling of 21235120685 in words is "twenty-one billion, two hundred thirty-five million, one hundred twenty thousand, six hundred eighty-five".