21240216 has 48 divisors (see below), whose sum is σ = 57922800. Its totient is φ = 7031232.

The previous prime is 21240211. The next prime is 21240221. The reversal of 21240216 is 61204212.

It is an interprime number because it is at equal distance from previous prime (21240211) and next prime (21240221).

It is a super-2 number, since 2×21240216² = 902293551453312, 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 (21240211) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 10365 + ... + 12243.

It is an arithmetic number, because the mean of its divisors is an integer number (1206725).

Almost surely, 2^21240216 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 21240216, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (28961400).

21240216 is an abundant number, since it is smaller than the sum of its proper divisors (36682584).

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

21240216 is a wasteful number, since it uses less digits than its factorization.

21240216 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2048 (or 2041 counting only the distinct ones).

The product of its (nonzero) digits is 192, while the sum is 18.

The square root of 21240216 is about 4608.7108826656. The cubic root of 21240216 is about 276.9403964951.

Adding to 21240216 its reverse (61204212), we get a palindrome (82444428).

The spelling of 21240216 in words is "twenty-one million, two hundred forty thousand, two hundred sixteen".