21655830 has 32 divisors (see below), whose sum is σ = 59399424. Its totient is φ = 4949856.

The previous prime is 21655817. The next prime is 21655847. The reversal of 21655830 is 3855612.

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

It is a Curzon number.

It is a congruent number.

It is an unprimeable number.

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, 51352 + ... + 51771.

It is an arithmetic number, because the mean of its divisors is an integer number (1856232).

Almost surely, 2^21655830 is an apocalyptic number.

21655830 is an abundant number, since it is smaller than the sum of its proper divisors (37743594).

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

21655830 is a wasteful number, since it uses less digits than its factorization.

21655830 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 103140.

The product of its (nonzero) digits is 7200, while the sum is 30.

The square root of 21655830 is about 4653.5824909418. The cubic root of 21655830 is about 278.7350679394.

The spelling of 21655830 in words is "twenty-one million, six hundred fifty-five thousand, eight hundred thirty".