21001111121 has 8 divisors (see below), whose sum is σ = 21044482920. Its totient is φ = 20957764608.

The previous prime is 21001111081. The next prime is 21001111181. The reversal of 21001111121 is 12111110012.

It can be written as a sum of positive squares in 4 ways, for example, as 11731272721 + 9269838400 = 108311^2 + 96280^2 .

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

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21001111121 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21001111181) 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, 3475715 + ... + 3481751.

It is an arithmetic number, because the mean of its divisors is an integer number (2630560365).

Almost surely, 2^21001111121 is an apocalyptic number.

It is an amenable number.

21001111121 is a deficient number, since it is larger than the sum of its proper divisors (43371799).

21001111121 is an equidigital number, since it uses as much as digits as its factorization.

21001111121 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 12643.

The product of its (nonzero) digits is 4, while the sum is 11.

Adding to 21001111121 its reverse (12111110012), we get a palindrome (33112221133).

The spelling of 21001111121 in words is "twenty-one billion, one million, one hundred eleven thousand, one hundred twenty-one".