21535665 has 16 divisors (see below), whose sum is σ = 35389248. Its totient is φ = 11174976.

The previous prime is 21535663. The next prime is 21535693. The reversal of 21535665 is 56653512.

It is not a de Polignac number, because 21535665 - 2¹ = 21535663 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21535663) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 18847 + ... + 19956.

It is an arithmetic number, because the mean of its divisors is an integer number (2211828).

Almost surely, 2^21535665 is an apocalyptic number.

It is an amenable number.

21535665 is a deficient number, since it is larger than the sum of its proper divisors (13853583).

21535665 is a wasteful number, since it uses less digits than its factorization.

21535665 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 38848.

The product of its digits is 27000, while the sum is 33.

The square root of 21535665 is about 4640.6535100134. The cubic root of 21535665 is about 278.2185581807.

The spelling of 21535665 in words is "twenty-one million, five hundred thirty-five thousand, six hundred sixty-five".