21289431 has 4 divisors (see below), whose sum is σ = 28385912. Its totient is φ = 14192952.

The previous prime is 21289409. The next prime is 21289439. The reversal of 21289431 is 13498212.

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

It is not a de Polignac number, because 21289431 - 2⁵ = 21289399 is a prime.

It is a super-2 number, since 2×21289431² = 906479744607522, 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 (21289439) 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, 3548236 + ... + 3548241.

It is an arithmetic number, because the mean of its divisors is an integer number (7096478).

Almost surely, 2^21289431 is an apocalyptic number.

21289431 is a deficient number, since it is larger than the sum of its proper divisors (7096481).

21289431 is an equidigital number, since it uses as much as digits as its factorization.

21289431 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7096480.

The product of its digits is 3456, while the sum is 30.

The square root of 21289431 is about 4614.0471389009. The cubic root of 21289431 is about 277.1541279724.

The spelling of 21289431 in words is "twenty-one million, two hundred eighty-nine thousand, four hundred thirty-one".