21008865 has 16 divisors (see below), whose sum is σ = 34041600. Its totient is φ = 11062272.

The previous prime is 21008857. The next prime is 21008879. The reversal of 21008865 is 56880012.

It is not a de Polignac number, because 21008865 - 2³ = 21008857 is a prime.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 7680 + ... + 10049.

It is an arithmetic number, because the mean of its divisors is an integer number (2127600).

Almost surely, 2^21008865 is an apocalyptic number.

It is an amenable number.

21008865 is a deficient number, since it is larger than the sum of its proper divisors (13032735).

21008865 is a wasteful number, since it uses less digits than its factorization.

21008865 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 17816.

The product of its (nonzero) digits is 3840, while the sum is 30.

The square root of 21008865 is about 4583.5428436963. The cubic root of 21008865 is about 275.9312341811.

Adding to 21008865 its reverse (56880012), we get a palindrome (77888877).

The spelling of 21008865 in words is "twenty-one million, eight thousand, eight hundred sixty-five".