21555930 has 64 divisors (see below), whose sum is σ = 57189888. Its totient is φ = 5156160.

The previous prime is 21555923. The next prime is 21555931. The reversal of 21555930 is 3955512.

It is a Harshad number since it is a multiple of its sum of digits (30).

It is not an unprimeable number, because it can be changed into a prime (21555931) 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 31 ways as a sum of consecutive naturals, for example, 26997 + ... + 27783.

It is an arithmetic number, because the mean of its divisors is an integer number (893592).

Almost surely, 2^21555930 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21555930, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (28594944).

21555930 is an abundant number, since it is smaller than the sum of its proper divisors (35633958).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21555930 is a wasteful number, since it uses less digits than its factorization.

21555930 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 891.

The product of its (nonzero) digits is 6750, while the sum is 30.

The square root of 21555930 is about 4642.8364175362. The cubic root of 21555930 is about 278.3057984482.

The spelling of 21555930 in words is "twenty-one million, five hundred fifty-five thousand, nine hundred thirty".