21000431 has 4 divisors (see below), whose sum is σ = 21129432. Its totient is φ = 20871432.

The previous prime is 21000407. The next prime is 21000433. The reversal of 21000431 is 13400012.

It is a happy number.

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 21000431 - 2⁶ = 21000367 is a prime.

It is a super-2 number, since 2×21000431² = 882036204371522, 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 (21000433) 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, 64256 + ... + 64581.

It is an arithmetic number, because the mean of its divisors is an integer number (5282358).

Almost surely, 2^21000431 is an apocalyptic number.

21000431 is a deficient number, since it is larger than the sum of its proper divisors (129001).

21000431 is a wasteful number, since it uses less digits than its factorization.

21000431 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 129000.

The product of its (nonzero) digits is 24, while the sum is 11.

The square root of 21000431 is about 4582.6227206699. The cubic root of 21000431 is about 275.8943050797.

Adding to 21000431 its reverse (13400012), we get a palindrome (34400443).

The spelling of 21000431 in words is "twenty-one million, four hundred thirty-one", and thus it is an aban number.