21001312121 has 4 divisors (see below), whose sum is σ = 21914412672. Its totient is φ = 20088211572.

The previous prime is 21001312109. The next prime is 21001312139. The reversal of 21001312121 is 12121310012.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21001312121 is a prime.

It is a super-2 number, since 2×21001312121² (a number of 21 digits) contains 22 as substring.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21001312096 and 21001312105.

It is not an unprimeable number, because it can be changed into a prime (21001312021) 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, 456550241 + ... + 456550286.

It is an arithmetic number, because the mean of its divisors is an integer number (5478603168).

Almost surely, 2^21001312121 is an apocalyptic number.

It is an amenable number.

21001312121 is a deficient number, since it is larger than the sum of its proper divisors (913100551).

21001312121 is an equidigital number, since it uses as much as digits as its factorization.

21001312121 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 913100550.

The product of its (nonzero) digits is 24, while the sum is 14.

Adding to 21001312121 its reverse (12121310012), we get a palindrome (33122622133).

The spelling of 21001312121 in words is "twenty-one billion, one million, three hundred twelve thousand, one hundred twenty-one".