21728425 has 6 divisors (see below), whose sum is σ = 26943278. Its totient is φ = 17382720.

The previous prime is 21728423. The next prime is 21728437. The reversal of 21728425 is 52482712.

It is a happy number.

It can be written as a sum of positive squares in 3 ways, for example, as 1827904 + 19900521 = 1352^2 + 4461^2 .

It is not a de Polignac number, because 21728425 - 2¹ = 21728423 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21728423) 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, 434544 + ... + 434593.

Almost surely, 2^21728425 is an apocalyptic number.

21728425 is a gapful number since it is divisible by the number (25) formed by its first and last digit.

It is an amenable number.

21728425 is a deficient number, since it is larger than the sum of its proper divisors (5214853).

21728425 is an equidigital number, since it uses as much as digits as its factorization.

21728425 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 869147 (or 869142 counting only the distinct ones).

The product of its digits is 8960, while the sum is 31.

The square root of 21728425 is about 4661.3758698479. The cubic root of 21728425 is about 279.0461805256.

The spelling of 21728425 in words is "twenty-one million, seven hundred twenty-eight thousand, four hundred twenty-five".