21007820 has 12 divisors (see below), whose sum is σ = 44116464. Its totient is φ = 8403120.

The previous prime is 21007813. The next prime is 21007837. The reversal of 21007820 is 2870012.

It is a Harshad number since it is a multiple of its sum of digits (20), and also a Moran number because the ratio is a prime number: 1050391 = 21007820 / (2 + 1 + 0 + 0 + 7 + 8 + 2 + 0).

It is a junction number, because it is equal to n+sod(n) for n = 21007792 and 21007801.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 525176 + ... + 525215.

It is an arithmetic number, because the mean of its divisors is an integer number (3676372).

Almost surely, 2^21007820 is an apocalyptic number.

21007820 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21007820 is an abundant number, since it is smaller than the sum of its proper divisors (23108644).

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

21007820 is a wasteful number, since it uses less digits than its factorization.

21007820 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1050400 (or 1050398 counting only the distinct ones).

The product of its (nonzero) digits is 224, while the sum is 20.

The square root of 21007820 is about 4583.4288474896. The cubic root of 21007820 is about 275.9266590819.

Adding to 21007820 its reverse (2870012), we get a palindrome (23877832).

The spelling of 21007820 in words is "twenty-one million, seven thousand, eight hundred twenty".