21020240 has 40 divisors (see below), whose sum is σ = 49365888. Its totient is φ = 8323200.

The previous prime is 21020239. The next prime is 21020267. The reversal of 21020240 is 4202012.

It is a tau number, because it is divible by the number of its divisors (40).

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 6965 + ... + 9515.

Almost surely, 2^21020240 is an apocalyptic number.

21020240 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 21020240, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (24682944).

21020240 is an abundant number, since it is smaller than the sum of its proper divisors (28345648).

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

21020240 is a wasteful number, since it uses less digits than its factorization.

21020240 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2667 (or 2661 counting only the distinct ones).

The product of its (nonzero) digits is 32, while the sum is 11.

The square root of 21020240 is about 4584.7835281505. The cubic root of 21020240 is about 275.9810250905.

Adding to 21020240 its reverse (4202012), we get a palindrome (25222252).

The spelling of 21020240 in words is "twenty-one million, twenty thousand, two hundred forty".