21724207 has 2 divisors, whose sum is σ = 21724208. Its totient is φ = 21724206.

The previous prime is 21724193. The next prime is 21724229. The reversal of 21724207 is 70242712.

It is a weak prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21724207 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21724007) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10862103 + 10862104.

It is an arithmetic number, because the mean of its divisors is an integer number (10862104).

Almost surely, 2^21724207 is an apocalyptic number.

21724207 is a deficient number, since it is larger than the sum of its proper divisors (1).

21724207 is an equidigital number, since it uses as much as digits as its factorization.

21724207 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 1568, while the sum is 25.

The square root of 21724207 is about 4660.9234063649. The cubic root of 21724207 is about 279.0281228744.

Adding to 21724207 its reverse (70242712), we get a palindrome (91966919).

The spelling of 21724207 in words is "twenty-one million, seven hundred twenty-four thousand, two hundred seven".