21109431 has 32 divisors (see below), whose sum is σ = 33392128. Its totient is φ = 11612160.

The previous prime is 21109409. The next prime is 21109441. The reversal of 21109431 is 13490112.

It is not a de Polignac number, because 21109431 - 2⁶ = 21109367 is a prime.

It is a super-2 number, since 2×21109431² = 891216154287522, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (21).

It is the 4595-th Hogben number.

It is a junction number, because it is equal to n+sod(n) for n = 21109398 and 21109407.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21109441) by changing a digit.

It is a nontrivial repunit in base 4594.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 87471 + ... + 87711.

It is an arithmetic number, because the mean of its divisors is an integer number (1043504).

Almost surely, 2^21109431 is an apocalyptic number.

21109431 is a gapful number since it is divisible by the number (21) formed by its first and last digit.

21109431 is a deficient number, since it is larger than the sum of its proper divisors (12282697).

21109431 is a wasteful number, since it uses less digits than its factorization.

21109431 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 391.

The product of its (nonzero) digits is 216, while the sum is 21.

The square root of 21109431 is about 4594.5000816193. The cubic root of 21109431 is about 276.3708127550.

Adding to 21109431 its reverse (13490112), we get a palindrome (34599543).

The spelling of 21109431 in words is "twenty-one million, one hundred nine thousand, four hundred thirty-one".