21147257 has 2 divisors, whose sum is σ = 21147258. Its totient is φ = 21147256.

The previous prime is 21147241. The next prime is 21147283. The reversal of 21147257 is 75274112.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 12243001 + 8904256 = 3499^2 + 2984^2 .

It is a cyclic number.

It is not a de Polignac number, because 21147257 - 2⁴ = 21147241 is a prime.

It is not a weakly prime, because it can be changed into another prime (21147157) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10573628 + 10573629.

It is an arithmetic number, because the mean of its divisors is an integer number (10573629).

Almost surely, 2^21147257 is an apocalyptic number.

It is an amenable number.

21147257 is a deficient number, since it is larger than the sum of its proper divisors (1).

21147257 is an equidigital number, since it uses as much as digits as its factorization.

21147257 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 3920, while the sum is 29.

The square root of 21147257 is about 4598.6146827061. The cubic root of 21147257 is about 276.5357905856.

The spelling of 21147257 in words is "twenty-one million, one hundred forty-seven thousand, two hundred fifty-seven".