21001001001221 has 4 divisors (see below), whose sum is σ = 21117028631244. Its totient is φ = 20884973371200.

The previous prime is 21001001001209. The next prime is 21001001001229. The reversal of 21001001001221 is 12210010010012.

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 7363158228196 + 13637842773025 = 2713514^2 + 3692945^2 .

It is a cyclic number.

It is not a de Polignac number, because 21001001001221 - 2²⁶ = 21000933892357 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 (21001001001229) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 58013814740 + ... + 58013815101.

It is an arithmetic number, because the mean of its divisors is an integer number (5279257157811).

Almost surely, 2^{21001001001221} is an apocalyptic number.

It is an amenable number.

21001001001221 is a deficient number, since it is larger than the sum of its proper divisors (116027630023).

21001001001221 is a wasteful number, since it uses less digits than its factorization.

21001001001221 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 116027630022.

The product of its (nonzero) digits is 8, while the sum is 11.

Adding to 21001001001221 its reverse (12210010010012), we get a palindrome (33211011011233).

The spelling of 21001001001221 in words is "twenty-one trillion, one billion, one million, one thousand, two hundred twenty-one".