21528657 has 6 divisors (see below), whose sum is σ = 31096962. Its totient is φ = 14352432.

The previous prime is 21528631. The next prime is 21528673. The reversal of 21528657 is 75682512.

It is a happy number.

It can be written as a sum of positive squares in only one way, i.e., 16966161 + 4562496 = 4119^2 + 2136^2 .

It is not a de Polignac number, because 21528657 - 2¹⁴ = 21512273 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21528257) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 1196028 + ... + 1196045.

It is an arithmetic number, because the mean of its divisors is an integer number (5182827).

Almost surely, 2^21528657 is an apocalyptic number.

It is an amenable number.

21528657 is a deficient number, since it is larger than the sum of its proper divisors (9568305).

21528657 is a wasteful number, since it uses less digits than its factorization.

21528657 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2392079 (or 2392076 counting only the distinct ones).

The product of its digits is 33600, while the sum is 36.

The square root of 21528657 is about 4639.8983825080. The cubic root of 21528657 is about 278.1883761983.

The spelling of 21528657 in words is "twenty-one million, five hundred twenty-eight thousand, six hundred fifty-seven".