21517320 has 64 divisors (see below), whose sum is σ = 70424640. Its totient is φ = 5216000.

The previous prime is 21517319. The next prime is 21517337. The reversal of 21517320 is 2371512.

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 15 ways as a sum of consecutive naturals, for example, 6831 + ... + 9470.

It is an arithmetic number, because the mean of its divisors is an integer number (1100385).

Almost surely, 2^21517320 is an apocalyptic number.

21517320 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21517320 is an abundant number, since it is smaller than the sum of its proper divisors (48907320).

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

21517320 is a wasteful number, since it uses less digits than its factorization.

21517320 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 16326 (or 16322 counting only the distinct ones).

The product of its (nonzero) digits is 420, while the sum is 21.

The square root of 21517320 is about 4638.6765353924. The cubic root of 21517320 is about 278.1395362516.

Adding to 21517320 its reverse (2371512), we get a palindrome (23888832).

The spelling of 21517320 in words is "twenty-one million, five hundred seventeen thousand, three hundred twenty".