21820656 has 180 divisors, whose sum is σ = 70882616. Its totient is φ = 5744640.

The previous prime is 21820633. The next prime is 21820661. The reversal of 21820656 is 65602812.

It is a super-2 number, since 2×21820656² = 952282056540672, which contains 22 as substring.

It is a congruent number.

It is an unprimeable number.

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 35 ways as a sum of consecutive naturals, for example, 1283560 + ... + 1283576.

Almost surely, 2^21820656 is an apocalyptic number.

21820656 is a gapful number since it is divisible by the number (26) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21820656, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (35441308).

21820656 is an abundant number, since it is smaller than the sum of its proper divisors (49061960).

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

21820656 is a wasteful number, since it uses less digits than its factorization.

21820656 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 80 (or 46 counting only the distinct ones).

The product of its (nonzero) digits is 5760, while the sum is 30.

The square root of 21820656 is about 4671.2585028020. The cubic root of 21820656 is about 279.4404471587.

The spelling of 21820656 in words is "twenty-one million, eight hundred twenty thousand, six hundred fifty-six".