21621216 has 24 divisors (see below), whose sum is σ = 56755944. Its totient is φ = 7207040.

The previous prime is 21621181. The next prime is 21621233. The reversal of 21621216 is 61212612.

It is a tau number, because it is divible by the number of its divisors (24).

It is a nude number because it is divisible by every one of its digits.

It is a junction number, because it is equal to n+sod(n) for n = 21621192 and 21621201.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 112515 + ... + 112706.

It is an arithmetic number, because the mean of its divisors is an integer number (2364831).

Almost surely, 2^21621216 is an apocalyptic number.

It is an amenable number.

21621216 is an abundant number, since it is smaller than the sum of its proper divisors (35134728).

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

21621216 is a wasteful number, since it uses less digits than its factorization.

21621216 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 225234 (or 225226 counting only the distinct ones).

The product of its digits is 288, while the sum is 21.

The square root of 21621216 is about 4649.8619334342. The cubic root of 21621216 is about 278.5864816135.

Adding to 21621216 its reverse (61212612), we get a palindrome (82833828).

The spelling of 21621216 in words is "twenty-one million, six hundred twenty-one thousand, two hundred sixteen".