21545005 has 4 divisors (see below), whose sum is σ = 25854012. Its totient is φ = 17236000.

The previous prime is 21545003. The next prime is 21545009. The reversal of 21545005 is 50054512.

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 14303524 + 7241481 = 3782^2 + 2691^2 .

It is not a de Polignac number, because 21545005 - 2¹ = 21545003 is a prime.

It is a Smith number, since the sum of its digits (22) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21545003) 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, 2154496 + ... + 2154505.

It is an arithmetic number, because the mean of its divisors is an integer number (6463503).

Almost surely, 2^21545005 is an apocalyptic number.

It is an amenable number.

21545005 is a deficient number, since it is larger than the sum of its proper divisors (4309007).

21545005 is an equidigital number, since it uses as much as digits as its factorization.

21545005 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4309006.

The product of its (nonzero) digits is 1000, while the sum is 22.

The square root of 21545005 is about 4641.6597247105. The cubic root of 21545005 is about 278.2587734199.

Adding to 21545005 its reverse (50054512), we get a palindrome (71599517).

The spelling of 21545005 in words is "twenty-one million, five hundred forty-five thousand, five".