21506565 has 16 divisors (see below), whose sum is σ = 34848000. Its totient is φ = 11324352.

The previous prime is 21506533. The next prime is 21506593. The reversal of 21506565 is 56560512.

It is not a de Polignac number, because 21506565 - 2⁵ = 21506533 is a prime.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 7890 + ... + 10259.

It is an arithmetic number, because the mean of its divisors is an integer number (2178000).

Almost surely, 2^21506565 is an apocalyptic number.

It is an amenable number.

21506565 is a deficient number, since it is larger than the sum of its proper divisors (13341435).

21506565 is a wasteful number, since it uses less digits than its factorization.

21506565 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 18236.

The product of its (nonzero) digits is 9000, while the sum is 30.

The square root of 21506565 is about 4637.5171158714. The cubic root of 21506565 is about 278.0931877093.

The spelling of 21506565 in words is "twenty-one million, five hundred six thousand, five hundred sixty-five".