21621020 has 12 divisors (see below), whose sum is σ = 45404184. Its totient is φ = 8648400.

The previous prime is 21621013. The next prime is 21621029. The reversal of 21621020 is 2012612.

It is a junction number, because it is equal to n+sod(n) for n = 21620986 and 21621004.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21621029) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 540506 + ... + 540545.

It is an arithmetic number, because the mean of its divisors is an integer number (3783682).

Almost surely, 2^21621020 is an apocalyptic number.

21621020 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21621020 is an abundant number, since it is smaller than the sum of its proper divisors (23783164).

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

21621020 is a wasteful number, since it uses less digits than its factorization.

21621020 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1081060 (or 1081058 counting only the distinct ones).

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

The square root of 21621020 is about 4649.8408574918. The cubic root of 21621020 is about 278.5856397997.

Adding to 21621020 its reverse (2012612), we get a palindrome (23633632).

The spelling of 21621020 in words is "twenty-one million, six hundred twenty-one thousand, twenty".