21305555 has 16 divisors (see below), whose sum is σ = 27125280. Its totient is φ = 16019712.

The previous prime is 21305551. The next prime is 21305563. The reversal of 21305555 is 55550312.

It is a cyclic number.

It is not a de Polignac number, because 21305555 - 2² = 21305551 is a prime.

21305555 is a modest number, since divided by 5555 gives 2130 as remainder.

It is not an unprimeable number, because it can be changed into a prime (21305551) 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 15 ways as a sum of consecutive naturals, for example, 12197 + ... + 13833.

It is an arithmetic number, because the mean of its divisors is an integer number (1695330).

Almost surely, 2^21305555 is an apocalyptic number.

21305555 is a deficient number, since it is larger than the sum of its proper divisors (5819725).

21305555 is a wasteful number, since it uses less digits than its factorization.

21305555 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1798.

The product of its (nonzero) digits is 3750, while the sum is 26.

The square root of 21305555 is about 4615.7940811956. The cubic root of 21305555 is about 277.2240798254.

Adding to 21305555 its reverse (55550312), we get a palindrome (76855867).

The spelling of 21305555 in words is "twenty-one million, three hundred five thousand, five hundred fifty-five".