21242431 has 12 divisors (see below), whose sum is σ = 24993360. Its totient is φ = 17999520.

The previous prime is 21242393. The next prime is 21242443. The reversal of 21242431 is 13424212.

It is not a de Polignac number, because 21242431 - 2¹⁵ = 21209663 is a prime.

It is a super-2 number, since 2×21242431² = 902481749579522, which contains 22 as substring.

It is a junction number, because it is equal to n+sod(n) for n = 21242399 and 21242408.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21242461) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 1926 + ... + 6796.

It is an arithmetic number, because the mean of its divisors is an integer number (2082780).

Almost surely, 2^21242431 is an apocalyptic number.

21242431 is a deficient number, since it is larger than the sum of its proper divisors (3750929).

21242431 is an equidigital number, since it uses as much as digits as its factorization.

21242431 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4974 (or 4967 counting only the distinct ones).

The product of its digits is 384, while the sum is 19.

The square root of 21242431 is about 4608.9511822105. The cubic root of 21242431 is about 276.9500229141.

Adding to 21242431 its reverse (13424212), we get a palindrome (34666643).

The spelling of 21242431 in words is "twenty-one million, two hundred forty-two thousand, four hundred thirty-one".