21556905 has 16 divisors (see below), whose sum is σ = 34581120. Its totient is φ = 11467008.

The previous prime is 21556891. The next prime is 21556907. The reversal of 21556905 is 50965512.

It is not a de Polignac number, because 21556905 - 2⁶ = 21556841 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21556907) by changing a digit.

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 15 ways as a sum of consecutive naturals, for example, 4836 + ... + 8154.

It is an arithmetic number, because the mean of its divisors is an integer number (2161320).

Almost surely, 2^21556905 is an apocalyptic number.

It is an amenable number.

21556905 is a deficient number, since it is larger than the sum of its proper divisors (13024215).

21556905 is a wasteful number, since it uses less digits than its factorization.

21556905 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3760.

The product of its (nonzero) digits is 13500, while the sum is 33.

The square root of 21556905 is about 4642.9414168176. The cubic root of 21556905 is about 278.3099944175.

The spelling of 21556905 in words is "twenty-one million, five hundred fifty-six thousand, nine hundred five".