21397947 has 4 divisors (see below), whose sum is σ = 28530600. Its totient is φ = 14265296.

The previous prime is 21397931. The next prime is 21397949. The reversal of 21397947 is 74979312.

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 21397947 - 2⁴ = 21397931 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21397899 and 21397908.

It is not an unprimeable number, because it can be changed into a prime (21397949) 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, 3566322 + ... + 3566327.

It is an arithmetic number, because the mean of its divisors is an integer number (7132650).

Almost surely, 2^21397947 is an apocalyptic number.

21397947 is a deficient number, since it is larger than the sum of its proper divisors (7132653).

21397947 is an equidigital number, since it uses as much as digits as its factorization.

21397947 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7132652.

The product of its digits is 95256, while the sum is 42.

The square root of 21397947 is about 4625.7914998409. The cubic root of 21397947 is about 277.6242313654.

The spelling of 21397947 in words is "twenty-one million, three hundred ninety-seven thousand, nine hundred forty-seven".