21605516 has 12 divisors (see below), whose sum is σ = 38184720. Its totient is φ = 10695600.

The previous prime is 21605509. The next prime is 21605531. The reversal of 21605516 is 61550612.

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, 26336 + ... + 27143.

It is an arithmetic number, because the mean of its divisors is an integer number (3182060).

Almost surely, 2^21605516 is an apocalyptic number.

It is an amenable number.

21605516 is a deficient number, since it is larger than the sum of its proper divisors (16579204).

21605516 is a wasteful number, since it uses less digits than its factorization.

21605516 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 53584 (or 53582 counting only the distinct ones).

The product of its (nonzero) digits is 1800, while the sum is 26.

The square root of 21605516 is about 4648.1734046827. The cubic root of 21605516 is about 278.5190344843.

The spelling of 21605516 in words is "twenty-one million, six hundred five thousand, five hundred sixteen".