21755520 has 128 divisors (see below), whose sum is σ = 77112000. Its totient is φ = 5796864.

The previous prime is 21755509. The next prime is 21755527. The reversal of 21755520 is 2555712.

It is a happy number.

It is a tau number, because it is divible by the number of its divisors (128).

It is a hoax number, since the sum of its digits (27) coincides with the sum of the digits of its distinct prime factors.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21755527) 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, 16651 + ... + 17909.

Almost surely, 2^21755520 is an apocalyptic number.

21755520 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 21755520, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (38556000).

21755520 is an abundant number, since it is smaller than the sum of its proper divisors (55356480).

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

21755520 is a wasteful number, since it uses less digits than its factorization.

21755520 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1287 (or 1269 counting only the distinct ones).

The product of its (nonzero) digits is 3500, while the sum is 27.

The square root of 21755520 is about 4664.2812951193. The cubic root of 21755520 is about 279.1621210616.

The spelling of 21755520 in words is "twenty-one million, seven hundred fifty-five thousand, five hundred twenty".