21121210021 has 8 divisors (see below), whose sum is σ = 21327937400. Its totient is φ = 20914718400.

The previous prime is 21121210007. The next prime is 21121210037. The reversal of 21121210021 is 12001212112.

It can be written as a sum of positive squares in 4 ways, for example, as 663629121 + 20457580900 = 25761^2 + 143030^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21121210021 - 2¹⁷ = 21121078949 is a prime.

It is a super-2 number, since 2×21121210021² (a number of 21 digits) contains 22 as substring.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21121209983 and 21121210010.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21121210421) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 123871 + ... + 239971.

It is an arithmetic number, because the mean of its divisors is an integer number (2665992175).

Almost surely, 2^21121210021 is an apocalyptic number.

It is an amenable number.

21121210021 is a deficient number, since it is larger than the sum of its proper divisors (206727379).

21121210021 is a wasteful number, since it uses less digits than its factorization.

21121210021 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 117879.

The product of its (nonzero) digits is 16, while the sum is 13.

Adding to 21121210021 its reverse (12001212112), we get a palindrome (33122422133).

The spelling of 21121210021 in words is "twenty-one billion, one hundred twenty-one million, two hundred ten thousand, twenty-one".