21305520 has 120 divisors (see below), whose sum is σ = 72423936. Its totient is φ = 5612544.

The previous prime is 21305513. The next prime is 21305533. The reversal of 21305520 is 2550312.

It is a happy number.

It is a tau number, because it is divible by the number of its divisors (120).

It is a super-3 number, since 3×21305520³ (a number of 23 digits) contains 333 as substring.

It is a Harshad number since it is a multiple of its sum of digits (18).

It is a junction number, because it is equal to n+sod(n) for n = 21305493 and 21305502.

It is an unprimeable number.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 91324 + ... + 91556.

Almost surely, 2^21305520 is an apocalyptic number.

21305520 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 21305520, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (36211968).

21305520 is an abundant number, since it is smaller than the sum of its proper divisors (51118416).

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

21305520 is a wasteful number, since it uses less digits than its factorization.

21305520 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 379 (or 370 counting only the distinct ones).

The product of its (nonzero) digits is 300, while the sum is 18.

The square root of 21305520 is about 4615.7902898637. The cubic root of 21305520 is about 277.2239280207.

Adding to 21305520 its reverse (2550312), we get a palindrome (23855832).

The spelling of 21305520 in words is "twenty-one million, three hundred five thousand, five hundred twenty".