21217516 has 24 divisors (see below), whose sum is σ = 38635520. Its totient is φ = 10184400.

The previous prime is 21217507. The next prime is 21217519. The reversal of 21217516 is 61571212.

It is not an unprimeable number, because it can be changed into a prime (21217519) by changing a digit.

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 7 ways as a sum of consecutive naturals, for example, 16621 + ... + 17851.

Almost surely, 2^21217516 is an apocalyptic number.

It is an amenable number.

21217516 is a deficient number, since it is larger than the sum of its proper divisors (17418004).

21217516 is a wasteful number, since it uses less digits than its factorization.

21217516 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1405 (or 1403 counting only the distinct ones).

The product of its digits is 840, while the sum is 25.

The square root of 21217516 is about 4606.2474966072. The cubic root of 21217516 is about 276.8417034017.

Adding to 21217516 its reverse (61571212), we get a palindrome (82788728).

The spelling of 21217516 in words is "twenty-one million, two hundred seventeen thousand, five hundred sixteen".