21216020 has 36 divisors (see below), whose sum is σ = 51830100. Its totient is φ = 7273728.

The previous prime is 21216011. The next prime is 21216047. The reversal of 21216020 is 2061212.

It can be written as a sum of positive squares in 2 ways, for example, as 7761796 + 13454224 = 2786^2 + 3668^2 .

It is a Harshad number since it is a multiple of its sum of digits (14).

It is a junction number, because it is equal to n+sod(n) for n = 21215986 and 21216004.

It is a congruent number.

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, 9845 + ... + 11804.

It is an arithmetic number, because the mean of its divisors is an integer number (1439725).

Almost surely, 2^21216020 is an apocalyptic number.

21216020 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21216020 is an abundant number, since it is smaller than the sum of its proper divisors (30614080).

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

21216020 is a wasteful number, since it uses less digits than its factorization.

21216020 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 21672 (or 21663 counting only the distinct ones).

The product of its (nonzero) digits is 48, while the sum is 14.

The square root of 21216020 is about 4606.0851055967. The cubic root of 21216020 is about 276.8351967506.

Adding to 21216020 its reverse (2061212), we get a palindrome (23277232).

The spelling of 21216020 in words is "twenty-one million, two hundred sixteen thousand, twenty".