21087665 has 16 divisors (see below), whose sum is σ = 26552448. Its totient is φ = 16046976.

The previous prime is 21087643. The next prime is 21087683. The reversal of 21087665 is 56678012.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21087665 is a prime.

It is a Duffinian number.

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 15 ways as a sum of consecutive naturals, for example, 26402 + ... + 27188.

It is an arithmetic number, because the mean of its divisors is an integer number (1659528).

Almost surely, 2^21087665 is an apocalyptic number.

It is an amenable number.

21087665 is a deficient number, since it is larger than the sum of its proper divisors (5464783).

21087665 is a wasteful number, since it uses less digits than its factorization.

21087665 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1048.

The product of its (nonzero) digits is 20160, while the sum is 35.

The square root of 21087665 is about 4592.1307690439. The cubic root of 21087665 is about 276.2757911534.

The spelling of 21087665 in words is "twenty-one million, eighty-seven thousand, six hundred sixty-five".