21216240 has 120 divisors (see below), whose sum is σ = 72346560. Its totient is φ = 5571072.

The previous prime is 21216203. The next prime is 21216241. The reversal of 21216240 is 4261212.

21216240 is a `hidden beast` number, since 21 + 21 + 624 + 0 = 666.

It is a tau number, because it is divible by the number of its divisors (120).

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 (21216241) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 56694 + ... + 57066.

It is an arithmetic number, because the mean of its divisors is an integer number (602888).

Almost surely, 2^21216240 is an apocalyptic number.

21216240 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21216240, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (36173280).

21216240 is an abundant number, since it is smaller than the sum of its proper divisors (51130320).

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

21216240 is a wasteful number, since it uses less digits than its factorization.

21216240 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 471 (or 462 counting only the distinct ones).

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

The square root of 21216240 is about 4606.1089869867. The cubic root of 21216240 is about 276.8361536302.

Adding to 21216240 its reverse (4261212), we get a palindrome (25477452).

The spelling of 21216240 in words is "twenty-one million, two hundred sixteen thousand, two hundred forty".