21055505 has 4 divisors (see below), whose sum is σ = 25266612. Its totient is φ = 16844400.

The previous prime is 21055501. The next prime is 21055513. The reversal of 21055505 is 50555012.

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 12103441 + 8952064 = 3479^2 + 2992^2 .

It is not a de Polignac number, because 21055505 - 2² = 21055501 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21055501) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2105546 + ... + 2105555.

It is an arithmetic number, because the mean of its divisors is an integer number (6316653).

Almost surely, 2^21055505 is an apocalyptic number.

It is an amenable number.

21055505 is a deficient number, since it is larger than the sum of its proper divisors (4211107).

21055505 is an equidigital number, since it uses as much as digits as its factorization.

21055505 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4211106.

The product of its (nonzero) digits is 1250, while the sum is 23.

The square root of 21055505 is about 4588.6277905274. The cubic root of 21055505 is about 276.1352737781.

The spelling of 21055505 in words is "twenty-one million, fifty-five thousand, five hundred five".