21217568 has 12 divisors (see below), whose sum is σ = 41772150. Its totient is φ = 10608768.

The previous prime is 21217561. The next prime is 21217571. The reversal of 21217568 is 86571212.

It can be written as a sum of positive squares in only one way, i.e., 17875984 + 3341584 = 4228^2 + 1828^2 .

It is a Harshad number since it is a multiple of its sum of digits (32), and also a Moran number because the ratio is a prime number: 663049 = 21217568 / (2 + 1 + 2 + 1 + 7 + 5 + 6 + 8).

It is not an unprimeable number, because it can be changed into a prime (21217561) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 331493 + ... + 331556.

Almost surely, 2^21217568 is an apocalyptic number.

It is an amenable number.

21217568 is a deficient number, since it is larger than the sum of its proper divisors (20554582).

21217568 is an equidigital number, since it uses as much as digits as its factorization.

21217568 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 663059 (or 663051 counting only the distinct ones).

The product of its digits is 6720, while the sum is 32.

The square root of 21217568 is about 4606.2531411115. The cubic root of 21217568 is about 276.8419295632.

The spelling of 21217568 in words is "twenty-one million, two hundred seventeen thousand, five hundred sixty-eight".