21405760 has 56 divisors (see below), whose sum is σ = 51425856. Its totient is φ = 8486400.

The previous prime is 21405749. The next prime is 21405773. The reversal of 21405760 is 6750412.

It is a super-2 number, since 2×21405760² = 916413122355200, which contains 22 as substring.

It is a hoax number, since the sum of its digits (25) coincides with the sum of the digits of its distinct prime factors.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 48099 + ... + 48541.

Almost surely, 2^21405760 is an apocalyptic number.

21405760 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 21405760, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (25712928).

21405760 is an abundant number, since it is smaller than the sum of its proper divisors (30020096).

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

21405760 is a wasteful number, since it uses less digits than its factorization.

21405760 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 611 (or 601 counting only the distinct ones).

The product of its (nonzero) digits is 1680, while the sum is 25.

The square root of 21405760 is about 4626.6359268912. The cubic root of 21405760 is about 277.6580167589.

The spelling of 21405760 in words is "twenty-one million, four hundred five thousand, seven hundred sixty".