21563172 has 30 divisors (see below), whose sum is σ = 56371238. Its totient is φ = 7187616.

The previous prime is 21563161. The next prime is 21563173. The reversal of 21563172 is 27136512.

It is a happy number.

21563172 is a `hidden beast` number, since 21 + 5 + 631 + 7 + 2 = 666.

It can be written as a sum of positive squares in only one way, i.e., 14561856 + 7001316 = 3816^2 + 2646^2 .

It is a Harshad number since it is a multiple of its sum of digits (27).

It is not an unprimeable number, because it can be changed into a prime (21563173) by changing a digit.

It is a polite number, since it can be written in 9 ways as a sum of consecutive naturals, for example, 32953 + ... + 33600.

Almost surely, 2^21563172 is an apocalyptic number.

It is an amenable number.

21563172 is an abundant number, since it is smaller than the sum of its proper divisors (34808066).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21563172 is a wasteful number, since it uses less digits than its factorization.

21563172 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 66569 (or 66558 counting only the distinct ones).

The product of its digits is 2520, while the sum is 27.

The square root of 21563172 is about 4643.6162632156. The cubic root of 21563172 is about 278.3369617975.

Adding to 21563172 its reverse (27136512), we get a palindrome (48699684).

The spelling of 21563172 in words is "twenty-one million, five hundred sixty-three thousand, one hundred seventy-two".