21500172 has 108 divisors (see below), whose sum is σ = 62014680. Its totient is φ = 6241536.

The previous prime is 21500161. The next prime is 21500177. The reversal of 21500172 is 27100512.

It is a Harshad number since it is a multiple of its sum of digits (18).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21500177) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 35 ways as a sum of consecutive naturals, for example, 499983 + ... + 500025.

It is an arithmetic number, because the mean of its divisors is an integer number (574210).

Almost surely, 2^21500172 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21500172, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (31007340).

21500172 is an abundant number, since it is smaller than the sum of its proper divisors (40514508).

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

21500172 is a wasteful number, since it uses less digits than its factorization.

21500172 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 132 (or 84 counting only the distinct ones).

The product of its (nonzero) digits is 140, while the sum is 18.

The square root of 21500172 is about 4636.8277949477. The cubic root of 21500172 is about 278.0656298305.

Adding to 21500172 its reverse (27100512), we get a palindrome (48600684).

It can be divided in two parts, 2150017 and 2, that multiplied together give a palindrome (4300034).

The spelling of 21500172 in words is "twenty-one million, five hundred thousand, one hundred seventy-two".