21240420 has 24 divisors (see below), whose sum is σ = 59473344. Its totient is φ = 5664096.

The previous prime is 21240403. The next prime is 21240433. The reversal of 21240420 is 2404212.

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

It is a self number, because there is not a number n which added to its sum of digits gives 21240420.

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, 176944 + ... + 177063.

It is an arithmetic number, because the mean of its divisors is an integer number (2478056).

Almost surely, 2^21240420 is an apocalyptic number.

21240420 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21240420 is an abundant number, since it is smaller than the sum of its proper divisors (38232924).

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

21240420 is a wasteful number, since it uses less digits than its factorization.

21240420 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 354019 (or 354017 counting only the distinct ones).

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

The square root of 21240420 is about 4608.7330146148. The cubic root of 21240420 is about 276.9412831098.

Adding to 21240420 its reverse (2404212), we get a palindrome (23644632).

The spelling of 21240420 in words is "twenty-one million, two hundred forty thousand, four hundred twenty".