21009216 has 28 divisors (see below), whose sum is σ = 55587392. Its totient is φ = 7003008.

The previous prime is 21009211. The next prime is 21009217. The reversal of 21009216 is 61290012.

It is a junction number, because it is equal to n+sod(n) for n = 21009192 and 21009201.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21009211) 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 3 ways as a sum of consecutive naturals, for example, 54520 + ... + 54903.

It is an arithmetic number, because the mean of its divisors is an integer number (1985264).

Almost surely, 2^21009216 is an apocalyptic number.

It is an amenable number.

21009216 is an abundant number, since it is smaller than the sum of its proper divisors (34578176).

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

21009216 is a wasteful number, since it uses less digits than its factorization.

21009216 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 109438 (or 109428 counting only the distinct ones).

The product of its (nonzero) digits is 216, while the sum is 21.

The square root of 21009216 is about 4583.5811326953. The cubic root of 21009216 is about 275.9327708550.

Adding to 21009216 its reverse (61290012), we get a palindrome (82299228).

The spelling of 21009216 in words is "twenty-one million, nine thousand, two hundred sixteen".