21220656 has 20 divisors (see below), whose sum is σ = 54820152. Its totient is φ = 7073536.

The previous prime is 21220649. The next prime is 21220687. The reversal of 21220656 is 65602212.

It is a Harshad number since it is a multiple of its sum of digits (24).

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 3 ways as a sum of consecutive naturals, for example, 221001 + ... + 221096.

Almost surely, 2^21220656 is an apocalyptic number.

It is an amenable number.

21220656 is an abundant number, since it is smaller than the sum of its proper divisors (33599496).

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

21220656 is a wasteful number, since it uses less digits than its factorization.

21220656 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 442108 (or 442102 counting only the distinct ones).

The product of its (nonzero) digits is 1440, while the sum is 24.

The square root of 21220656 is about 4606.5883254313. The cubic root of 21220656 is about 276.8553594154.

Adding to 21220656 its reverse (65602212), we get a palindrome (86822868).

The spelling of 21220656 in words is "twenty-one million, two hundred twenty thousand, six hundred fifty-six".