21084431 has 4 divisors (see below), whose sum is σ = 21399192. Its totient is φ = 20769672.

The previous prime is 21084419. The next prime is 21084451. The reversal of 21084431 is 13448012.

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 21084431 - 2¹⁸ = 20822287 is a prime.

It is a super-2 number, since 2×21084431² = 889106461187522, which contains 22 as substring.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21084397 and 21084406.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21084451) 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, 157280 + ... + 157413.

It is an arithmetic number, because the mean of its divisors is an integer number (5349798).

Almost surely, 2^21084431 is an apocalyptic number.

21084431 is a deficient number, since it is larger than the sum of its proper divisors (314761).

21084431 is an equidigital number, since it uses as much as digits as its factorization.

21084431 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 314760.

The product of its (nonzero) digits is 768, while the sum is 23.

The square root of 21084431 is about 4591.7786314238. The cubic root of 21084431 is about 276.2616672318.

The spelling of 21084431 in words is "twenty-one million, eighty-four thousand, four hundred thirty-one".