21521212221 has 16 divisors (see below), whose sum is σ = 28753882560. Its totient is φ = 14318040960.

The previous prime is 21521212213. The next prime is 21521212261. The reversal of 21521212221 is 12221212512.

It is not a de Polignac number, because 21521212221 - 2³ = 21521212213 is a prime.

It is a super-2 number, since 2×21521212221² (a number of 21 digits) contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21521212261) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 3680326 + ... + 3686168.

It is an arithmetic number, because the mean of its divisors is an integer number (1797117660).

Almost surely, 2^21521212221 is an apocalyptic number.

It is an amenable number.

21521212221 is a deficient number, since it is larger than the sum of its proper divisors (7232670339).

21521212221 is a wasteful number, since it uses less digits than its factorization.

21521212221 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 8156.

The product of its digits is 320, while the sum is 21.

Adding to 21521212221 its reverse (12221212512), we get a palindrome (33742424733).

The spelling of 21521212221 in words is "twenty-one billion, five hundred twenty-one million, two hundred twelve thousand, two hundred twenty-one".