21085663 has 4 divisors (see below), whose sum is σ = 21203640. Its totient is φ = 20967688.

The previous prime is 21085643. The next prime is 21085703. The reversal of 21085663 is 36658012.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21085663 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21085643) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 58720 + ... + 59077.

It is an arithmetic number, because the mean of its divisors is an integer number (5300910).

Almost surely, 2^21085663 is an apocalyptic number.

21085663 is a deficient number, since it is larger than the sum of its proper divisors (117977).

21085663 is a wasteful number, since it uses less digits than its factorization.

21085663 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 117976.

The product of its (nonzero) digits is 8640, while the sum is 31.

The square root of 21085663 is about 4591.9127822728. The cubic root of 21085663 is about 276.2670479436.

The spelling of 21085663 in words is "twenty-one million, eighty-five thousand, six hundred sixty-three".