21247145 has 4 divisors (see below), whose sum is σ = 25496580. Its totient is φ = 16997712.

The previous prime is 21247133. The next prime is 21247151. The reversal of 21247145 is 54174212.

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

It can be written as a sum of positive squares in 2 ways, for example, as 8743849 + 12503296 = 2957^2 + 3536^2 .

It is a cyclic number.

It is not a de Polignac number, because 21247145 - 2⁶ = 21247081 is a prime.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2124710 + ... + 2124719.

It is an arithmetic number, because the mean of its divisors is an integer number (6374145).

Almost surely, 2^21247145 is an apocalyptic number.

It is an amenable number.

21247145 is a deficient number, since it is larger than the sum of its proper divisors (4249435).

21247145 is an equidigital number, since it uses as much as digits as its factorization.

21247145 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4249434.

The product of its digits is 2240, while the sum is 26.

The square root of 21247145 is about 4609.4625500160. The cubic root of 21247145 is about 276.9705077925.

The spelling of 21247145 in words is "twenty-one million, two hundred forty-seven thousand, one hundred forty-five".