21106555 has 4 divisors (see below), whose sum is σ = 25327872. Its totient is φ = 16885240.

The previous prime is 21106543. The next prime is 21106573. The reversal of 21106555 is 55560112.

It is a semiprime because it is the product of two primes.

It is not a de Polignac number, because 21106555 - 2⁵ = 21106523 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 (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2110651 + ... + 2110660.

It is an arithmetic number, because the mean of its divisors is an integer number (6331968).

Almost surely, 2^21106555 is an apocalyptic number.

21106555 is a deficient number, since it is larger than the sum of its proper divisors (4221317).

21106555 is an equidigital number, since it uses as much as digits as its factorization.

21106555 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4221316.

The product of its (nonzero) digits is 1500, while the sum is 25.

The square root of 21106555 is about 4594.1870880494. The cubic root of 21106555 is about 276.3582610420.

Adding to 21106555 its reverse (55560112), we get a palindrome (76666667).

The spelling of 21106555 in words is "twenty-one million, one hundred six thousand, five hundred fifty-five".