21121001221 has 4 divisors (see below), whose sum is σ = 21519510732. Its totient is φ = 20722491712.

The previous prime is 21121001207. The next prime is 21121001233. The reversal of 21121001221 is 12210012112.

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 13264128900 + 7856872321 = 115170^2 + 88639^2 .

It is a cyclic number.

It is not a de Polignac number, because 21121001221 - 2¹³ = 21120993029 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21121001201) 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, 199254676 + ... + 199254781.

It is an arithmetic number, because the mean of its divisors is an integer number (5379877683).

Almost surely, 2^21121001221 is an apocalyptic number.

It is an amenable number.

21121001221 is a deficient number, since it is larger than the sum of its proper divisors (398509511).

21121001221 is an equidigital number, since it uses as much as digits as its factorization.

21121001221 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 398509510.

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

Adding to 21121001221 its reverse (12210012112), we get a palindrome (33331013333).

The spelling of 21121001221 in words is "twenty-one billion, one hundred twenty-one million, one thousand, two hundred twenty-one".