21555505 has 4 divisors (see below), whose sum is σ = 25866612. Its totient is φ = 17244400.

The previous prime is 21555503. The next prime is 21555511. The reversal of 21555505 is 50555512.

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 16613776 + 4941729 = 4076^2 + 2223^2 .

It is not a de Polignac number, because 21555505 - 2¹ = 21555503 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21555503) by changing a digit.

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, 2155546 + ... + 2155555.

It is an arithmetic number, because the mean of its divisors is an integer number (6466653).

Almost surely, 2^21555505 is an apocalyptic number.

It is an amenable number.

21555505 is a deficient number, since it is larger than the sum of its proper divisors (4311107).

21555505 is an equidigital number, since it uses as much as digits as its factorization.

21555505 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4311106.

The product of its (nonzero) digits is 6250, while the sum is 28.

The square root of 21555505 is about 4642.7906478755. The cubic root of 21555505 is about 278.3039693964.

The spelling of 21555505 in words is "twenty-one million, five hundred fifty-five thousand, five hundred five".