21131213221 has 4 divisors (see below), whose sum is σ = 21131636332. Its totient is φ = 21130790112.

The previous prime is 21131213161. The next prime is 21131213239. The reversal of 21131213221 is 12231213112.

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 13476888100 + 7654325121 = 116090^2 + 87489^2 .

It is a cyclic number.

It is not a de Polignac number, because 21131213221 - 2¹⁷ = 21131082149 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21131213021) 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, 124776 + ... + 240481.

It is an arithmetic number, because the mean of its divisors is an integer number (5282909083).

Almost surely, 2^21131213221 is an apocalyptic number.

It is an amenable number.

21131213221 is a deficient number, since it is larger than the sum of its proper divisors (423111).

21131213221 is an equidigital number, since it uses as much as digits as its factorization.

21131213221 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 423110.

The product of its digits is 144, while the sum is 19.

Adding to 21131213221 its reverse (12231213112), we get a palindrome (33362426333).

The spelling of 21131213221 in words is "twenty-one billion, one hundred thirty-one million, two hundred thirteen thousand, two hundred twenty-one".