21011231 has 2 divisors, whose sum is σ = 21011232. Its totient is φ = 21011230.

The previous prime is 21011191. The next prime is 21011233. The reversal of 21011231 is 13211012.

It is a strong prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21011231 is a prime.

It is a super-2 number, since 2×21011231² = 882943656270722, which contains 22 as substring.

Together with 21011233, it forms a pair of twin primes.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21011233) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10505615 + 10505616.

It is an arithmetic number, because the mean of its divisors is an integer number (10505616).

Almost surely, 2^21011231 is an apocalyptic number.

21011231 is a deficient number, since it is larger than the sum of its proper divisors (1).

21011231 is an equidigital number, since it uses as much as digits as its factorization.

21011231 is an evil number, because the sum of its binary digits is even.

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

The square root of 21011231 is about 4583.8009337230. The cubic root of 21011231 is about 275.9415921703.

Adding to 21011231 its reverse (13211012), we get a palindrome (34222243).

The spelling of 21011231 in words is "twenty-one million, eleven thousand, two hundred thirty-one".