21228240 has 240 divisors, whose sum is σ = 78369984. Its totient is φ = 4730880.

The previous prime is 21228227. The next prime is 21228247. The reversal of 21228240 is 4282212.

It is a happy number.

It is a tau number, because it is divible by the number of its divisors (240).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21228247) by changing a digit.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 493659 + ... + 493701.

Almost surely, 2^21228240 is an apocalyptic number.

21228240 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 21228240, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (39184992).

21228240 is an abundant number, since it is smaller than the sum of its proper divisors (57141744).

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

21228240 is a wasteful number, since it uses less digits than its factorization.

21228240 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 98 (or 81 counting only the distinct ones).

The product of its (nonzero) digits is 512, while the sum is 21.

The square root of 21228240 is about 4607.4114207438. The cubic root of 21228240 is about 276.8883370476. Note that the first 3 decimals are identical.

The spelling of 21228240 in words is "twenty-one million, two hundred twenty-eight thousand, two hundred forty".