21573216 has 240 divisors, whose sum is σ = 76839840. Its totient is φ = 5806080.

The previous prime is 21573203. The next prime is 21573239. The reversal of 21573216 is 61237512.

It is a happy number.

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

It is a self number, because there is not a number n which added to its sum of digits gives 21573216.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 39 ways as a sum of consecutive naturals, for example, 526156 + ... + 526196.

It is an arithmetic number, because the mean of its divisors is an integer number (320166).

Almost surely, 2^21573216 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 21573216, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (38419920).

21573216 is an abundant number, since it is smaller than the sum of its proper divisors (55266624).

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

21573216 is a wasteful number, since it uses less digits than its factorization.

21573216 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 99 (or 82 counting only the distinct ones).

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

The square root of 21573216 is about 4644.6976220202. The cubic root of 21573216 is about 278.3801710015.

The spelling of 21573216 in words is "twenty-one million, five hundred seventy-three thousand, two hundred sixteen".