21216560 has 20 divisors (see below), whose sum is σ = 49328688. Its totient is φ = 8486592.

The previous prime is 21216553. The next prime is 21216607. The reversal of 21216560 is 6561212.

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

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 132524 + ... + 132683.

Almost surely, 2^21216560 is an apocalyptic number.

21216560 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21216560 is an abundant number, since it is smaller than the sum of its proper divisors (28112128).

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

21216560 is a wasteful number, since it uses less digits than its factorization.

21216560 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 265220 (or 265214 counting only the distinct ones).

The product of its (nonzero) digits is 720, while the sum is 23.

The square root of 21216560 is about 4606.1437233330. The cubic root of 21216560 is about 276.8375454433.

Adding to 21216560 its reverse (6561212), we get a palindrome (27777772).

The spelling of 21216560 in words is "twenty-one million, two hundred sixteen thousand, five hundred sixty".