21665385 has 48 divisors (see below), whose sum is σ = 43380480. Its totient is φ = 9797760.

The previous prime is 21665383. The next prime is 21665389. The reversal of 21665385 is 58356612.

21665385 is a `hidden beast` number, since 216 + 65 + 385 = 666.

It is not a de Polignac number, because 21665385 - 2¹ = 21665383 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21665383) by changing a digit.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 34020 + ... + 34650.

It is an arithmetic number, because the mean of its divisors is an integer number (903760).

Almost surely, 2^21665385 is an apocalyptic number.

It is an amenable number.

21665385 is a primitive abundant number, since it is smaller than the sum of its proper divisors, none of which is abundant.

21665385 is a wasteful number, since it uses less digits than its factorization.

21665385 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 758 (or 755 counting only the distinct ones).

The product of its digits is 43200, while the sum is 36.

The square root of 21665385 is about 4654.6090061357. The cubic root of 21665385 is about 278.7760564702.

The spelling of 21665385 in words is "twenty-one million, six hundred sixty-five thousand, three hundred eighty-five".