21638810 has 8 divisors (see below), whose sum is σ = 38949876. Its totient is φ = 8655520.

The previous prime is 21638809. The next prime is 21638819. The reversal of 21638810 is 1883612.

It can be written as a sum of positive squares in 2 ways, for example, as 20894041 + 744769 = 4571^2 + 863^2 .

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

It is a super-2 number, since 2×21638810² = 936476196432200, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (21638819) 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, 1081931 + ... + 1081950.

Almost surely, 2^21638810 is an apocalyptic number.

21638810 is a deficient number, since it is larger than the sum of its proper divisors (17311066).

21638810 is a wasteful number, since it uses less digits than its factorization.

21638810 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2163888.

The product of its (nonzero) digits is 2304, while the sum is 29.

The square root of 21638810 is about 4651.7534328466. The cubic root of 21638810 is about 278.6620265730.

The spelling of 21638810 in words is "twenty-one million, six hundred thirty-eight thousand, eight hundred ten".