21728268 has 18 divisors (see below), whose sum is σ = 54924324. Its totient is φ = 7242744.

The previous prime is 21728249. The next prime is 21728269. The reversal of 21728268 is 86282712.

It is a happy number.

It is a tau number, because it is divible by the number of its divisors (18).

It is a Harshad number since it is a multiple of its sum of digits (36), and also a Moran number because the ratio is a prime number: 603563 = 21728268 / (2 + 1 + 7 + 2 + 8 + 2 + 6 + 8).

It is not an unprimeable number, because it can be changed into a prime (21728269) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 301746 + ... + 301817.

Almost surely, 2^21728268 is an apocalyptic number.

It is an amenable number.

21728268 is an abundant number, since it is smaller than the sum of its proper divisors (33196056).

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

21728268 is a wasteful number, since it uses less digits than its factorization.

21728268 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 603573 (or 603568 counting only the distinct ones).

The product of its digits is 21504, while the sum is 36.

The square root of 21728268 is about 4661.3590292961. The cubic root of 21728268 is about 279.0455084358.

It can be divided in two parts, 2172 and 8268, that added together give a triangular number (10440 = T₁₄₄).

The spelling of 21728268 in words is "twenty-one million, seven hundred twenty-eight thousand, two hundred sixty-eight".