21728115 has 64 divisors (see below), whose sum is σ = 41817600. Its totient is φ = 10668672.

The previous prime is 21728111. The next prime is 21728129. The reversal of 21728115 is 51182712.

It is not a de Polignac number, because 21728115 - 2² = 21728111 is a prime.

It is a super-3 number, since 3×21728115³ (a number of 23 digits) contains 333 as substring. Note that it is a super-d number also for d = 2.

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

It is not an unprimeable number, because it can be changed into a prime (21728111) by changing a digit.

It is a polite number, since it can be written in 63 ways as a sum of consecutive naturals, for example, 110197 + ... + 110393.

It is an arithmetic number, because the mean of its divisors is an integer number (653400).

Almost surely, 2^21728115 is an apocalyptic number.

21728115 is a deficient number, since it is larger than the sum of its proper divisors (20089485).

21728115 is a wasteful number, since it uses less digits than its factorization.

21728115 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 273 (or 267 counting only the distinct ones).

The product of its digits is 1120, while the sum is 27.

The square root of 21728115 is about 4661.3426177444. The cubic root of 21728115 is about 279.0448534663.

The spelling of 21728115 in words is "twenty-one million, seven hundred twenty-eight thousand, one hundred fifteen".