21125820 has 24 divisors (see below), whose sum is σ = 59152464. Its totient is φ = 5633536.

The previous prime is 21125803. The next prime is 21125843. The reversal of 21125820 is 2852112.

It is a happy number.

It is a congruent number.

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, 175989 + ... + 176108.

It is an arithmetic number, because the mean of its divisors is an integer number (2464686).

Almost surely, 2^21125820 is an apocalyptic number.

21125820 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21125820 is an abundant number, since it is smaller than the sum of its proper divisors (38026644).

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

21125820 is a wasteful number, since it uses less digits than its factorization.

21125820 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 352109 (or 352107 counting only the distinct ones).

The product of its (nonzero) digits is 320, while the sum is 21.

The square root of 21125820 is about 4596.2832810870. The cubic root of 21125820 is about 276.4423174387.

Adding to 21125820 its reverse (2852112), we get a palindrome (23977932).

It can be divided in two parts, 21125 and 820, that added together give a triangular number (21945 = T₂₀₉).

The spelling of 21125820 in words is "twenty-one million, one hundred twenty-five thousand, eight hundred twenty".