21001001231 has 4 divisors (see below), whose sum is σ = 24001144272. Its totient is φ = 18000858192.

The previous prime is 21001001227. The next prime is 21001001239. The reversal of 21001001231 is 13210010012.

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

It is a cyclic number.

It is not a de Polignac number, because 21001001231 - 2² = 21001001227 is a prime.

It is a super-2 number, since 2×21001001231² (a number of 21 digits) contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21001001239) 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, 1500071510 + ... + 1500071523.

It is an arithmetic number, because the mean of its divisors is an integer number (6000286068).

Almost surely, 2^21001001231 is an apocalyptic number.

21001001231 is a deficient number, since it is larger than the sum of its proper divisors (3000143041).

21001001231 is an equidigital number, since it uses as much as digits as its factorization.

21001001231 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3000143040.

The product of its (nonzero) digits is 12, while the sum is 11.

Adding to 21001001231 its reverse (13210010012), we get a palindrome (34211011243).

The spelling of 21001001231 in words is "twenty-one billion, one million, one thousand, two hundred thirty-one".