21605680 has 20 divisors (see below), whose sum is σ = 50233392. Its totient is φ = 8642240.

The previous prime is 21605677. The next prime is 21605693. The reversal of 21605680 is 8650612.

It is a tau number, because it is divible by the number of its divisors (20).

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 3 ways as a sum of consecutive naturals, for example, 134956 + ... + 135115.

Almost surely, 2^21605680 is an apocalyptic number.

21605680 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21605680 is an abundant number, since it is smaller than the sum of its proper divisors (28627712).

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

21605680 is a wasteful number, since it uses less digits than its factorization.

21605680 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 270084 (or 270078 counting only the distinct ones).

The product of its (nonzero) digits is 2880, while the sum is 28.

The square root of 21605680 is about 4648.1910459877. The cubic root of 21605680 is about 278.5197391964.

The spelling of 21605680 in words is "twenty-one million, six hundred five thousand, six hundred eighty".