21145505 has 4 divisors (see below), whose sum is σ = 25374612. Its totient is φ = 16916400.

The previous prime is 21145489. The next prime is 21145511. The reversal of 21145505 is 50554112.

It is a happy number.

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 15618304 + 5527201 = 3952^2 + 2351^2 .

It is not a de Polignac number, because 21145505 - 2⁴ = 21145489 is a prime.

It is a Duffinian number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2114546 + ... + 2114555.

It is an arithmetic number, because the mean of its divisors is an integer number (6343653).

Almost surely, 2^21145505 is an apocalyptic number.

It is an amenable number.

21145505 is a deficient number, since it is larger than the sum of its proper divisors (4229107).

21145505 is an equidigital number, since it uses as much as digits as its factorization.

21145505 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4229106.

The product of its (nonzero) digits is 1000, while the sum is 23.

The square root of 21145505 is about 4598.4241866100. The cubic root of 21145505 is about 276.5281535969.

Adding to 21145505 its reverse (50554112), we get a palindrome (71699617).

The spelling of 21145505 in words is "twenty-one million, one hundred forty-five thousand, five hundred five".