21207420 has 240 divisors, whose sum is σ = 76839840. Its totient is φ = 4852224.

The previous prime is 21207377. The next prime is 21207421. The reversal of 21207420 is 2470212.

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 = 21207393 and 21207402.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21207421) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 79 ways as a sum of consecutive naturals, for example, 400114 + ... + 400166.

It is an arithmetic number, because the mean of its divisors is an integer number (320166).

Almost surely, 2^21207420 is an apocalyptic number.

21207420 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 21207420, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (38419920).

21207420 is an abundant number, since it is smaller than the sum of its proper divisors (55632420).

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

21207420 is a wasteful number, since it uses less digits than its factorization.

21207420 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 106 (or 95 counting only the distinct ones).

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

The square root of 21207420 is about 4605.1514633072. The cubic root of 21207420 is about 276.7977862710.

Adding to 21207420 its reverse (2470212), we get a palindrome (23677632).

The spelling of 21207420 in words is "twenty-one million, two hundred seven thousand, four hundred twenty".