21206847121 has 4 divisors (see below), whose sum is σ = 21208414500. Its totient is φ = 21205279744.

The previous prime is 21206847097. The next prime is 21206847127. The reversal of 21206847121 is 12174860212.

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 11916778896 + 9290068225 = 109164^2 + 96385^2 .

It is a cyclic number.

It is not a de Polignac number, because 21206847121 - 2⁵ = 21206847089 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21206847127) 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, 763216 + ... + 790513.

It is an arithmetic number, because the mean of its divisors is an integer number (5302103625).

Almost surely, 2^21206847121 is an apocalyptic number.

It is an amenable number.

21206847121 is a deficient number, since it is larger than the sum of its proper divisors (1567379).

21206847121 is a wasteful number, since it uses less digits than its factorization.

21206847121 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1567378.

The product of its (nonzero) digits is 10752, while the sum is 34.

The spelling of 21206847121 in words is "twenty-one billion, two hundred six million, eight hundred forty-seven thousand, one hundred twenty-one".