21010820 has 24 divisors (see below), whose sum is σ = 45316824. Its totient is φ = 8176896.

The previous prime is 21010811. The next prime is 21010831. The reversal of 21010820 is 2801012.

It can be written as a sum of positive squares in 4 ways, for example, as 12166144 + 8844676 = 3488^2 + 2974^2 .

It is a junction number, because it is equal to n+sod(n) for n = 21010795 and 21010804.

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, 13457 + ... + 14936.

It is an arithmetic number, because the mean of its divisors is an integer number (1888201).

Almost surely, 2^21010820 is an apocalyptic number.

21010820 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21010820 is an abundant number, since it is smaller than the sum of its proper divisors (24306004).

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

21010820 is a wasteful number, since it uses less digits than its factorization.

21010820 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 28439 (or 28437 counting only the distinct ones).

The product of its (nonzero) digits is 32, while the sum is 14.

The square root of 21010820 is about 4583.7561017140. The cubic root of 21010820 is about 275.9397929304.

Adding to 21010820 its reverse (2801012), we get a palindrome (23811832).

The spelling of 21010820 in words is "twenty-one million, ten thousand, eight hundred twenty".