21728427 has 16 divisors (see below), whose sum is σ = 34179072. Its totient is φ = 12015360.

The previous prime is 21728423. The next prime is 21728437. The reversal of 21728427 is 72482712.

It is not a de Polignac number, because 21728427 - 2² = 21728423 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21728423) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 16038 + ... + 17339.

It is an arithmetic number, because the mean of its divisors is an integer number (2136192).

Almost surely, 2^21728427 is an apocalyptic number.

21728427 is a deficient number, since it is larger than the sum of its proper divisors (12450645).

21728427 is a wasteful number, since it uses less digits than its factorization.

21728427 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 33418.

The product of its digits is 12544, while the sum is 33.

The square root of 21728427 is about 4661.3760843768. The cubic root of 21728427 is about 279.0461890872.

It can be divided in two parts, 21728 and 427, that added together give a triangular number (22155 = T₂₁₀).

The spelling of 21728427 in words is "twenty-one million, seven hundred twenty-eight thousand, four hundred twenty-seven".