21257947 has 4 divisors (see below), whose sum is σ = 21288640. Its totient is φ = 21227256.

The previous prime is 21257933. The next prime is 21257963. The reversal of 21257947 is 74975212.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 21257947 - 2¹⁵ = 21225179 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21257927) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 14283 + ... + 15700.

It is an arithmetic number, because the mean of its divisors is an integer number (5322160).

Almost surely, 2^21257947 is an apocalyptic number.

21257947 is a deficient number, since it is larger than the sum of its proper divisors (30693).

21257947 is an equidigital number, since it uses as much as digits as its factorization.

21257947 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 30692.

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

The square root of 21257947 is about 4610.6341212462. The cubic root of 21257947 is about 277.0174368984.

The spelling of 21257947 in words is "twenty-one million, two hundred fifty-seven thousand, nine hundred forty-seven".