21001369685 has 4 divisors (see below), whose sum is σ = 25201643628. Its totient is φ = 16801095744.

The previous prime is 21001369661. The next prime is 21001369723. The reversal of 21001369685 is 58696310012.

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 10330892881 + 10670476804 = 101641^2 + 103298^2 .

It is a cyclic number.

It is not a de Polignac number, because 21001369685 - 2¹⁸ = 21001107541 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, 2100136964 + ... + 2100136973.

It is an arithmetic number, because the mean of its divisors is an integer number (6300410907).

Almost surely, 2^21001369685 is an apocalyptic number.

It is an amenable number.

21001369685 is a deficient number, since it is larger than the sum of its proper divisors (4200273943).

21001369685 is an equidigital number, since it uses as much as digits as its factorization.

21001369685 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4200273942.

The product of its (nonzero) digits is 77760, while the sum is 41.

Adding to 21001369685 its reverse (58696310012), we get a palindrome (79697679697).

The spelling of 21001369685 in words is "twenty-one billion, one million, three hundred sixty-nine thousand, six hundred eighty-five".