21821520 has 160 divisors (see below), whose sum is σ = 79994880. Its totient is φ = 4815360.

The previous prime is 21821507. The next prime is 21821533. The reversal of 21821520 is 2512812.

It is a happy number.

It is an interprime number because it is at equal distance from previous prime (21821507) and next prime (21821533).

It is a super-2 number, since 2×21821520² = 952357470220800, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (21).

It is a congruent number.

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 31 ways as a sum of consecutive naturals, for example, 51871 + ... + 52289.

It is an arithmetic number, because the mean of its divisors is an integer number (499968).

Almost surely, 2^21821520 is an apocalyptic number.

21821520 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21821520, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (39997440).

21821520 is an abundant number, since it is smaller than the sum of its proper divisors (58173360).

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

21821520 is a wasteful number, since it uses less digits than its factorization.

21821520 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 473 (or 467 counting only the distinct ones).

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

The square root of 21821520 is about 4671.3509823176. The cubic root of 21821520 is about 279.4441353056. Note that the first 3 decimals are identical.

The spelling of 21821520 in words is "twenty-one million, eight hundred twenty-one thousand, five hundred twenty".