21765520 has 40 divisors (see below), whose sum is σ = 57835584. Its totient is φ = 7462272.

The previous prime is 21765517. The next prime is 21765529. The reversal of 21765520 is 2556712.

It is a tau number, because it is divible by the number of its divisors (40).

It is a Harshad number since it is a multiple of its sum of digits (28).

It is not an unprimeable number, because it can be changed into a prime (21765529) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 18874 + ... + 19993.

Almost surely, 2^21765520 is an apocalyptic number.

21765520 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21765520 is an abundant number, since it is smaller than the sum of its proper divisors (36070064).

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

21765520 is a wasteful number, since it uses less digits than its factorization.

21765520 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 38887 (or 38881 counting only the distinct ones).

The product of its (nonzero) digits is 4200, while the sum is 28.

The square root of 21765520 is about 4665.3531484765. The cubic root of 21765520 is about 279.2048871212.

The spelling of 21765520 in words is "twenty-one million, seven hundred sixty-five thousand, five hundred twenty".