21521442121 has 4 divisors (see below), whose sum is σ = 21524964244. Its totient is φ = 21517920000.

The previous prime is 21521442091. The next prime is 21521442169. The reversal of 21521442121 is 12124412512.

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 1452753225 + 20068688896 = 38115^2 + 141664^2 .

It is a cyclic number.

It is not a de Polignac number, because 21521442121 - 2⁹ = 21521441609 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21521442521) 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, 1751880 + ... + 1764121.

It is an arithmetic number, because the mean of its divisors is an integer number (5381241061).

Almost surely, 2^21521442121 is an apocalyptic number.

It is an amenable number.

21521442121 is a deficient number, since it is larger than the sum of its proper divisors (3522123).

21521442121 is an equidigital number, since it uses as much as digits as its factorization.

21521442121 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3522122.

The product of its digits is 1280, while the sum is 25.

Adding to 21521442121 its reverse (12124412512), we get a palindrome (33645854633).

The spelling of 21521442121 in words is "twenty-one billion, five hundred twenty-one million, four hundred forty-two thousand, one hundred twenty-one".