21021020221 has 4 divisors (see below), whose sum is σ = 21102814332. Its totient is φ = 20939226112.

The previous prime is 21021020161. The next prime is 21021020239. The reversal of 21021020221 is 12202012012.

It is a happy number.

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 14979067321 + 6041952900 = 122389^2 + 77730^2 .

It is a cyclic number.

It is not a de Polignac number, because 21021020221 - 2⁹ = 21021019709 is a prime.

It is a super-2 number, since 2×21021020221² (a number of 21 digits) contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21021020621) 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, 40896670 + ... + 40897183.

It is an arithmetic number, because the mean of its divisors is an integer number (5275703583).

Almost surely, 2^21021020221 is an apocalyptic number.

It is an amenable number.

21021020221 is a deficient number, since it is larger than the sum of its proper divisors (81794111).

21021020221 is an equidigital number, since it uses as much as digits as its factorization.

21021020221 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 81794110.

The product of its (nonzero) digits is 32, while the sum is 13.

Adding to 21021020221 its reverse (12202012012), we get a palindrome (33223032233).

The spelling of 21021020221 in words is "twenty-one billion, twenty-one million, twenty thousand, two hundred twenty-one".