21497257 has 2 divisors, whose sum is σ = 21497258. Its totient is φ = 21497256.

The previous prime is 21497213. The next prime is 21497269. The reversal of 21497257 is 75279412.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 21492496 + 4761 = 4636^2 + 69^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21497257 is a prime.

It is not a weakly prime, because it can be changed into another prime (21497057) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10748628 + 10748629.

It is an arithmetic number, because the mean of its divisors is an integer number (10748629).

Almost surely, 2^21497257 is an apocalyptic number.

It is an amenable number.

21497257 is a deficient number, since it is larger than the sum of its proper divisors (1).

21497257 is an equidigital number, since it uses as much as digits as its factorization.

21497257 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 35280, while the sum is 37.

The square root of 21497257 is about 4636.5134530162. The cubic root of 21497257 is about 278.0530625210.

The spelling of 21497257 in words is "twenty-one million, four hundred ninety-seven thousand, two hundred fifty-seven".