21545172 has 72 divisors (see below), whose sum is σ = 60907392. Its totient is φ = 6364800.

The previous prime is 21545149. The next prime is 21545179. The reversal of 21545172 is 27154512.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21545179) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 15573 + ... + 16899.

It is an arithmetic number, because the mean of its divisors is an integer number (845936).

Almost surely, 2^21545172 is an apocalyptic number.

21545172 is a gapful number since it is divisible by the number (22) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21545172, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (30453696).

21545172 is an abundant number, since it is smaller than the sum of its proper divisors (39362220).

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

21545172 is a wasteful number, since it uses less digits than its factorization.

21545172 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1389 (or 1384 counting only the distinct ones).

The product of its digits is 2800, while the sum is 27.

The square root of 21545172 is about 4641.6777139306. The cubic root of 21545172 is about 278.2594923661.

Adding to 21545172 its reverse (27154512), we get a palindrome (48699684).

It can be divided in two parts, 2154517 and 2, that multiplied together give a palindrome (4309034).

The spelling of 21545172 in words is "twenty-one million, five hundred forty-five thousand, one hundred seventy-two".