21455545 has 4 divisors (see below), whose sum is σ = 25746660. Its totient is φ = 17164432.

The previous prime is 21455543. The next prime is 21455549. The reversal of 21455545 is 54555412.

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 7772944 + 13682601 = 2788^2 + 3699^2 .

It is a cyclic number.

It is not a de Polignac number, because 21455545 - 2¹ = 21455543 is a prime.

It is a super-2 number, since 2×21455545² = 920680822494050, which contains 22 as substring.

It is a Smith number, since the sum of its digits (31) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is not an unprimeable number, because it can be changed into a prime (21455543) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2145550 + ... + 2145559.

It is an arithmetic number, because the mean of its divisors is an integer number (6436665).

Almost surely, 2^21455545 is an apocalyptic number.

It is an amenable number.

21455545 is a deficient number, since it is larger than the sum of its proper divisors (4291115).

21455545 is an equidigital number, since it uses as much as digits as its factorization.

21455545 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4291114.

The product of its digits is 20000, while the sum is 31.

The square root of 21455545 is about 4632.0130612942. The cubic root of 21455545 is about 277.8731068660.

The spelling of 21455545 in words is "twenty-one million, four hundred fifty-five thousand, five hundred forty-five".