21431243 has 4 divisors (see below), whose sum is σ = 21929688. Its totient is φ = 20932800.

The previous prime is 21431231. The next prime is 21431269. The reversal of 21431243 is 34213412.

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

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21431243 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21436243) 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, 249158 + ... + 249243.

It is an arithmetic number, because the mean of its divisors is an integer number (5482422).

Almost surely, 2^21431243 is an apocalyptic number.

21431243 is a deficient number, since it is larger than the sum of its proper divisors (498445).

21431243 is an equidigital number, since it uses as much as digits as its factorization.

21431243 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 498444.

The product of its digits is 576, while the sum is 20.

The square root of 21431243 is about 4629.3890525641. The cubic root of 21431243 is about 277.7681546118.

Adding to 21431243 its reverse (34213412), we get a palindrome (55644655).

The spelling of 21431243 in words is "twenty-one million, four hundred thirty-one thousand, two hundred forty-three".