21090555 has 48 divisors (see below), whose sum is σ = 38413440. Its totient is φ = 10692864.

The previous prime is 21090547. The next prime is 21090583. The reversal of 21090555 is 55509012.

21090555 is a `hidden beast` number, since 2 + 109 + 0 + 555 = 666.

It is not a de Polignac number, because 21090555 - 2³ = 21090547 is a prime.

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 47 ways as a sum of consecutive naturals, for example, 88126 + ... + 88364.

It is an arithmetic number, because the mean of its divisors is an integer number (800280).

Almost surely, 2^21090555 is an apocalyptic number.

21090555 is a deficient number, since it is larger than the sum of its proper divisors (17322885).

21090555 is a wasteful number, since it uses less digits than its factorization.

21090555 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 340 (or 337 counting only the distinct ones).

The product of its (nonzero) digits is 2250, while the sum is 27.

The square root of 21090555 is about 4592.4454270029. The cubic root of 21090555 is about 276.2884114944.

Adding to 21090555 its reverse (55509012), we get a palindrome (76599567).

The spelling of 21090555 in words is "twenty-one million, ninety thousand, five hundred fifty-five".