21018240 has 192 divisors, whose sum is σ = 75184200. Its totient is φ = 5406720.

The previous prime is 21018229. The next prime is 21018241. The reversal of 21018240 is 4281012.

It can be written as a sum of positive squares in 4 ways, for example, as 7884864 + 13133376 = 2808^2 + 3624^2 .

It is a tau number, because it is divible by the number of its divisors (192).

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 (21018241) 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, 236116 + ... + 236204.

Almost surely, 2^21018240 is an apocalyptic number.

21018240 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 21018240, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (37592100).

21018240 is an abundant number, since it is smaller than the sum of its proper divisors (54165960).

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

21018240 is a wasteful number, since it uses less digits than its factorization.

21018240 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 155 (or 140 counting only the distinct ones).

The product of its (nonzero) digits is 128, while the sum is 18.

The square root of 21018240 is about 4584.5654101561. The cubic root of 21018240 is about 275.9722719466.

Adding to 21018240 its reverse (4281012), we get a palindrome (25299252).

The spelling of 21018240 in words is "twenty-one million, eighteen thousand, two hundred forty".