21011221001 has 4 divisors (see below), whose sum is σ = 21012377604. Its totient is φ = 21010064400.

The previous prime is 21011220983. The next prime is 21011221019. The reversal of 21011221001 is 10012211012.

It is a semiprime because it is the product of two primes.

It is an interprime number because it is at equal distance from previous prime (21011220983) and next prime (21011221019).

It can be written as a sum of positive squares in 2 ways, for example, as 9545094601 + 11466126400 = 97699^2 + 107080^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21011221001 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21011221031) 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, 550610 + ... + 587531.

It is an arithmetic number, because the mean of its divisors is an integer number (5253094401).

Almost surely, 2^21011221001 is an apocalyptic number.

It is an amenable number.

21011221001 is a deficient number, since it is larger than the sum of its proper divisors (1156603).

21011221001 is a wasteful number, since it uses less digits than its factorization.

21011221001 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1156602.

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

Adding to 21011221001 its reverse (10012211012), we get a palindrome (31023432013).

The spelling of 21011221001 in words is "twenty-one billion, eleven million, two hundred twenty-one thousand, one".