21213121221 has 6 divisors (see below), whose sum is σ = 30641175110. Its totient is φ = 14142080808.

The previous prime is 21213121217. The next prime is 21213121229. The reversal of 21213121221 is 12212131212.

It can be written as a sum of positive squares in only one way, i.e., 14049360900 + 7163760321 = 118530^2 + 84639^2 .

It is not a de Polignac number, because 21213121221 - 2² = 21213121217 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21213121194 and 21213121203.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21213121229) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 1178506726 + ... + 1178506743.

Almost surely, 2^21213121221 is an apocalyptic number.

It is an amenable number.

21213121221 is a deficient number, since it is larger than the sum of its proper divisors (9428053889).

21213121221 is a wasteful number, since it uses less digits than its factorization.

21213121221 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2357013475 (or 2357013472 counting only the distinct ones).

The product of its digits is 96, while the sum is 18.

Adding to 21213121221 its reverse (12212131212), we get a palindrome (33425252433).

Subtracting from 21213121221 its reverse (12212131212), we obtain a palindrome (9000990009).

The spelling of 21213121221 in words is "twenty-one billion, two hundred thirteen million, one hundred twenty-one thousand, two hundred twenty-one".