21105031 has 4 divisors (see below), whose sum is σ = 21158064. Its totient is φ = 21052000.

The previous prime is 21105023. The next prime is 21105043. The reversal of 21105031 is 13050112.

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 21105031 - 2³ = 21105023 is a prime.

It is a super-2 number, since 2×21105031² = 890844667021922, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21105431) 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, 25915 + ... + 26716.

It is an arithmetic number, because the mean of its divisors is an integer number (5289516).

Almost surely, 2^21105031 is an apocalyptic number.

21105031 is a deficient number, since it is larger than the sum of its proper divisors (53033).

21105031 is an equidigital number, since it uses as much as digits as its factorization.

21105031 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 53032.

The product of its (nonzero) digits is 30, while the sum is 13.

The square root of 21105031 is about 4594.0212232858. The cubic root of 21105031 is about 276.3516093940.

Adding to 21105031 its reverse (13050112), we get a palindrome (34155143).

The spelling of 21105031 in words is "twenty-one million, one hundred five thousand, thirty-one".