21007145 has 4 divisors (see below), whose sum is σ = 25208580. Its totient is φ = 16805712.

The previous prime is 21007139. The next prime is 21007153. The reversal of 21007145 is 54170012.

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 13808656 + 7198489 = 3716^2 + 2683^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21007145 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, 2100710 + ... + 2100719.

It is an arithmetic number, because the mean of its divisors is an integer number (6302145).

Almost surely, 2^21007145 is an apocalyptic number.

It is an amenable number.

21007145 is a deficient number, since it is larger than the sum of its proper divisors (4201435).

21007145 is an equidigital number, since it uses as much as digits as its factorization.

21007145 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4201434.

The product of its (nonzero) digits is 280, while the sum is 20.

The square root of 21007145 is about 4583.3552120690. The cubic root of 21007145 is about 275.9237037937.

Adding to 21007145 its reverse (54170012), we get a palindrome (75177157).

The spelling of 21007145 in words is "twenty-one million, seven thousand, one hundred forty-five".