21312132221 has 4 divisors (see below), whose sum is σ = 21315907932. Its totient is φ = 21308356512.

The previous prime is 21312132203. The next prime is 21312132251. The reversal of 21312132221 is 12223121312.

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 13214652025 + 8097480196 = 114955^2 + 89986^2 .

It is a cyclic number.

It is not a de Polignac number, because 21312132221 - 2¹⁴ = 21312115837 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21312132193 and 21312132202.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21312132251) 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, 1879376 + ... + 1890681.

It is an arithmetic number, because the mean of its divisors is an integer number (5328976983).

Almost surely, 2^21312132221 is an apocalyptic number.

It is an amenable number.

21312132221 is a deficient number, since it is larger than the sum of its proper divisors (3775711).

21312132221 is an equidigital number, since it uses as much as digits as its factorization.

21312132221 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3775710.

The product of its digits is 288, while the sum is 20.

Adding to 21312132221 its reverse (12223121312), we get a palindrome (33535253533).

The spelling of 21312132221 in words is "twenty-one billion, three hundred twelve million, one hundred thirty-two thousand, two hundred twenty-one".