21516820 has 24 divisors (see below), whose sum is σ = 48661704. Its totient is φ = 7944576.

The previous prime is 21516791. The next prime is 21516827. The reversal of 21516820 is 2861512.

It can be written as a sum of positive squares in 4 ways, for example, as 3437316 + 18079504 = 1854^2 + 4252^2 .

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21516827) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 41119 + ... + 41638.

It is an arithmetic number, because the mean of its divisors is an integer number (2027571).

Almost surely, 2^21516820 is an apocalyptic number.

21516820 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21516820 is an abundant number, since it is smaller than the sum of its proper divisors (27144884).

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

21516820 is a wasteful number, since it uses less digits than its factorization.

21516820 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 82779 (or 82777 counting only the distinct ones).

The product of its (nonzero) digits is 960, while the sum is 25.

The square root of 21516820 is about 4638.6226403966. The cubic root of 21516820 is about 278.1373818500.

The spelling of 21516820 in words is "twenty-one million, five hundred sixteen thousand, eight hundred twenty".