21706637 has 4 divisors (see below), whose sum is σ = 22983516. Its totient is φ = 20429760.

The previous prime is 21706609. The next prime is 21706639. The reversal of 21706637 is 73660712.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 19307236 + 2399401 = 4394^2 + 1549^2 .

It is a cyclic number.

It is not a de Polignac number, because 21706637 - 2⁸ = 21706381 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 (21706639) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 638414 + ... + 638447.

It is an arithmetic number, because the mean of its divisors is an integer number (5745879).

Almost surely, 2^21706637 is an apocalyptic number.

It is an amenable number.

21706637 is a deficient number, since it is larger than the sum of its proper divisors (1276879).

21706637 is a wasteful number, since it uses less digits than its factorization.

21706637 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1276878.

The product of its (nonzero) digits is 10584, while the sum is 32.

The square root of 21706637 is about 4659.0382054669. The cubic root of 21706637 is about 278.9528789097.

The spelling of 21706637 in words is "twenty-one million, seven hundred six thousand, six hundred thirty-seven".