21655420 has 48 divisors (see below), whose sum is σ = 47900160. Its totient is φ = 8207936.

The previous prime is 21655393. The next prime is 21655423. The reversal of 21655420 is 2455612.

It is a zygodrome in base 9.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21655423) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 82209 + ... + 82471.

It is an arithmetic number, because the mean of its divisors is an integer number (997920).

Almost surely, 2^21655420 is an apocalyptic number.

21655420 is a gapful number since it is divisible by the number (20) 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 21655420, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (23950080).

21655420 is an abundant number, since it is smaller than the sum of its proper divisors (26244740).

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

21655420 is a wasteful number, since it uses less digits than its factorization.

21655420 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 474 (or 472 counting only the distinct ones).

The product of its (nonzero) digits is 2400, while the sum is 25.

The square root of 21655420 is about 4653.5384386507. The cubic root of 21655420 is about 278.7333088734.

The spelling of 21655420 in words is "twenty-one million, six hundred fifty-five thousand, four hundred twenty".