20724257 has 2 divisors, whose sum is σ = 20724258. Its totient is φ = 20724256.

The previous prime is 20724251. The next prime is 20724259. The reversal of 20724257 is 75242702.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 11182336 + 9541921 = 3344^2 + 3089^2 .

It is a cyclic number.

It is not a de Polignac number, because 20724257 - 2⁸ = 20724001 is a prime.

Together with 20724259, it forms a pair of twin primes.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (20724251) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10362128 + 10362129.

It is an arithmetic number, because the mean of its divisors is an integer number (10362129).

Almost surely, 2^20724257 is an apocalyptic number.

It is an amenable number.

20724257 is a deficient number, since it is larger than the sum of its proper divisors (1).

20724257 is an equidigital number, since it uses as much as digits as its factorization.

20724257 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 7840, while the sum is 29.

The square root of 20724257 is about 4552.3902512856. The cubic root of 20724257 is about 274.6795473885.

Adding to 20724257 its reverse (75242702), we get a palindrome (95966959).

The spelling of 20724257 in words is "twenty million, seven hundred twenty-four thousand, two hundred fifty-seven".