21042240 has 112 divisors (see below), whose sum is σ = 69787008. Its totient is φ = 5361664.

The previous prime is 21042223. The next prime is 21042251. The reversal of 21042240 is 4224012.

It is a Harshad number since it is a multiple of its sum of digits (15).

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 21604 + ... + 22556.

Almost surely, 2^21042240 is an apocalyptic number.

21042240 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 21042240, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (34893504).

21042240 is an abundant number, since it is smaller than the sum of its proper divisors (48744768).

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

21042240 is a wasteful number, since it uses less digits than its factorization.

21042240 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 996 (or 986 counting only the distinct ones).

The product of its (nonzero) digits is 128, while the sum is 15.

The square root of 21042240 is about 4587.1821415767. The cubic root of 21042240 is about 276.0772730495.

Adding to 21042240 its reverse (4224012), we get a palindrome (25266252).

The spelling of 21042240 in words is "twenty-one million, forty-two thousand, two hundred forty".