21006216 has 160 divisors (see below), whose sum is σ = 73529280. Its totient is φ = 5443200.

The previous prime is 21006163. The next prime is 21006217. The reversal of 21006216 is 61260012.

It is a happy number.

It is a super-2 number, since 2×21006216² = 882522221277312, which contains 22 as substring.

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 (21006217) by changing a digit.

It is a polite number, since it can be written in 39 ways as a sum of consecutive naturals, for example, 49686 + ... + 50106.

It is an arithmetic number, because the mean of its divisors is an integer number (459558).

Almost surely, 2^21006216 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 21006216, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (36764640).

21006216 is an abundant number, since it is smaller than the sum of its proper divisors (52523064).

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

21006216 is a wasteful number, since it uses less digits than its factorization.

21006216 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 457 (or 444 counting only the distinct ones).

The product of its (nonzero) digits is 144, while the sum is 18.

The square root of 21006216 is about 4583.2538659778. The cubic root of 21006216 is about 275.9196363379.

Adding to 21006216 its reverse (61260012), we get a palindrome (82266228).

The spelling of 21006216 in words is "twenty-one million, six thousand, two hundred sixteen".