21731243 has 2 divisors, whose sum is σ = 21731244. Its totient is φ = 21731242.

The previous prime is 21731239. The next prime is 21731257. The reversal of 21731243 is 34213712.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21731243 - 2² = 21731239 is a prime.

It is a Sophie Germain prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (21731263) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10865621 + 10865622.

It is an arithmetic number, because the mean of its divisors is an integer number (10865622).

Almost surely, 2^21731243 is an apocalyptic number.

21731243 is a deficient number, since it is larger than the sum of its proper divisors (1).

21731243 is an equidigital number, since it uses as much as digits as its factorization.

21731243 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 1008, while the sum is 23.

The square root of 21731243 is about 4661.6781313171. The cubic root of 21731243 is about 279.0582433442.

Adding to 21731243 its reverse (34213712), we get a palindrome (55944955).

The spelling of 21731243 in words is "twenty-one million, seven hundred thirty-one thousand, two hundred forty-three".