21506709 has 32 divisors (see below), whose sum is σ = 33839104. Its totient is φ = 11897280.

The previous prime is 21506707. The next prime is 21506729. The reversal of 21506709 is 90760512.

It is not a de Polignac number, because 21506709 - 2¹ = 21506707 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21506707) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 131862 + ... + 132024.

It is an arithmetic number, because the mean of its divisors is an integer number (1057472).

Almost surely, 2^21506709 is an apocalyptic number.

It is an amenable number.

21506709 is a deficient number, since it is larger than the sum of its proper divisors (12332395).

21506709 is a wasteful number, since it uses less digits than its factorization.

21506709 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 337.

The product of its (nonzero) digits is 3780, while the sum is 30.

The square root of 21506709 is about 4637.5326413946. The cubic root of 21506709 is about 278.0938083776.

The spelling of 21506709 in words is "twenty-one million, five hundred six thousand, seven hundred nine".