21518820 has 36 divisors (see below), whose sum is σ = 65274300. Its totient is φ = 5738304.

The previous prime is 21518813. The next prime is 21518837. The reversal of 21518820 is 2881512.

It can be written as a sum of positive squares in 2 ways, for example, as 10188864 + 11329956 = 3192^2 + 3366^2 .

It is a tau number, because it is divible by the number of its divisors (36).

It is a super-2 number, since 2×21518820² = 926119228384800, which contains 22 as substring.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 59595 + ... + 59954.

It is an arithmetic number, because the mean of its divisors is an integer number (1813175).

Almost surely, 2^21518820 is an apocalyptic number.

21518820 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21518820 is an abundant number, since it is smaller than the sum of its proper divisors (43755480).

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

21518820 is a wasteful number, since it uses less digits than its factorization.

21518820 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 119564 (or 119559 counting only the distinct ones).

The product of its (nonzero) digits is 1280, while the sum is 27.

The square root of 21518820 is about 4638.8382166228. The cubic root of 21518820 is about 278.1459992561.

The spelling of 21518820 in words is "twenty-one million, five hundred eighteen thousand, eight hundred twenty".