21520420 has 24 divisors (see below), whose sum is σ = 45662904. Its totient is φ = 8518656.

The previous prime is 21520399. The next prime is 21520423. The reversal of 21520420 is 2402512.

It can be written as a sum of positive squares in 4 ways, for example, as 4562496 + 16957924 = 2136^2 + 4118^2 .

It is a junction number, because it is equal to n+sod(n) for n = 21520394 and 21520403.

It is not an unprimeable number, because it can be changed into a prime (21520423) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 3607 + ... + 7486.

It is an arithmetic number, because the mean of its divisors is an integer number (1902621).

Almost surely, 2^21520420 is an apocalyptic number.

21520420 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21520420 is an abundant number, since it is smaller than the sum of its proper divisors (24142484).

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

21520420 is a wasteful number, since it uses less digits than its factorization.

21520420 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 11199 (or 11197 counting only the distinct ones).

The product of its (nonzero) digits is 160, while the sum is 16.

The square root of 21520420 is about 4639.0106703908. The cubic root of 21520420 is about 278.1528927966.

Adding to 21520420 its reverse (2402512), we get a palindrome (23922932).

The spelling of 21520420 in words is "twenty-one million, five hundred twenty thousand, four hundred twenty".