21212121021 has 72 divisors (see below), whose sum is σ = 36855643680. Its totient is φ = 10802623104.

The previous prime is 21212120987. The next prime is 21212121023. The reversal of 21212121021 is 12012121212.

It is not a de Polignac number, because 21212121021 - 2⁹ = 21212120509 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21212121023) by changing a digit.

It is a polite number, since it can be written in 71 ways as a sum of consecutive naturals, for example, 705726 + ... + 735168.

It is an arithmetic number, because the mean of its divisors is an integer number (511883940).

Almost surely, 2^21212121021 is an apocalyptic number.

21212121021 is a gapful number since it is divisible by the number (21) formed by its first and last digit.

It is an amenable number.

21212121021 is a deficient number, since it is larger than the sum of its proper divisors (15643522659).

21212121021 is a wasteful number, since it uses less digits than its factorization.

21212121021 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 29515 (or 29495 counting only the distinct ones).

The product of its (nonzero) digits is 32, while the sum is 15.

Adding to 21212121021 its reverse (12012121212), we get a palindrome (33224242233).

The spelling of 21212121021 in words is "twenty-one billion, two hundred twelve million, one hundred twenty-one thousand, twenty-one".