21021212021 has 4 divisors (see below), whose sum is σ = 21130130412. Its totient is φ = 20912293632.

The previous prime is 21021211987. The next prime is 21021212041. The reversal of 21021212021 is 12021212012.

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 3818004100 + 17203207921 = 61790^2 + 131161^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21021212021 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21021211987 and 21021212005.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21021212041) 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, 54458906 + ... + 54459291.

It is an arithmetic number, because the mean of its divisors is an integer number (5282532603).

Almost surely, 2^21021212021 is an apocalyptic number.

It is an amenable number.

21021212021 is a deficient number, since it is larger than the sum of its proper divisors (108918391).

21021212021 is a wasteful number, since it uses less digits than its factorization.

21021212021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 108918390.

The product of its (nonzero) digits is 32, while the sum is 14.

Adding to 21021212021 its reverse (12021212012), we get a palindrome (33042424033).

Subtracting from 21021212021 its reverse (12021212012), we obtain a palindrome (9000000009).

The spelling of 21021212021 in words is "twenty-one billion, twenty-one million, two hundred twelve thousand, twenty-one".