21240720 has 60 divisors (see below), whose sum is σ = 71335836. Its totient is φ = 5664000.

The previous prime is 21240719. The next prime is 21240743. The reversal of 21240720 is 2704212.

It can be written as a sum of positive squares in 2 ways, for example, as 8020224 + 13220496 = 2832^2 + 3636^2 .

It is a tau number, because it is divible by the number of its divisors (60).

It is a super-2 number, since 2×21240720² = 902336372236800, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (18).

It is a junction number, because it is equal to n+sod(n) for n = 21240693 and 21240702.

It is an unprimeable number.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 14031 + ... + 15470.

Almost surely, 2^21240720 is an apocalyptic number.

21240720 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21240720 is an abundant number, since it is smaller than the sum of its proper divisors (50095116).

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

21240720 is a wasteful number, since it uses less digits than its factorization.

21240720 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 29520 (or 29511 counting only the distinct ones).

The product of its (nonzero) digits is 224, while the sum is 18.

The square root of 21240720 is about 4608.7655614058. The cubic root of 21240720 is about 276.9425869445.

Adding to 21240720 its reverse (2704212), we get a palindrome (23944932).

The spelling of 21240720 in words is "twenty-one million, two hundred forty thousand, seven hundred twenty".