21637906 has 8 divisors (see below), whose sum is σ = 34366140. Its totient is φ = 10182528.

The previous prime is 21637877. The next prime is 21637909. The reversal of 21637906 is 60973612.

It can be written as a sum of positive squares in 2 ways, for example, as 20930625 + 707281 = 4575^2 + 841^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is a Harshad number since it is a multiple of its sum of digits (34), and also a Moran number because the ratio is a prime number: 636409 = 21637906 / (2 + 1 + 6 + 3 + 7 + 9 + 0 + 6).

It is not an unprimeable number, because it can be changed into a prime (21637909) 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, 318171 + ... + 318238.

Almost surely, 2^21637906 is an apocalyptic number.

21637906 is a deficient number, since it is larger than the sum of its proper divisors (12728234).

21637906 is a wasteful number, since it uses less digits than its factorization.

21637906 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 636428.

The product of its (nonzero) digits is 13608, while the sum is 34.

The square root of 21637906 is about 4651.6562641709. The cubic root of 21637906 is about 278.6581459841.

The spelling of 21637906 in words is "twenty-one million, six hundred thirty-seven thousand, nine hundred six".