21071663 has 4 divisors (see below), whose sum is σ = 21585648. Its totient is φ = 20557680.

The previous prime is 21071647. The next prime is 21071683. The reversal of 21071663 is 36617012.

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

It is a cyclic number.

It is not a de Polignac number, because 21071663 - 2⁴ = 21071647 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 (21071683) 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, 256931 + ... + 257012.

It is an arithmetic number, because the mean of its divisors is an integer number (5396412).

Almost surely, 2^21071663 is an apocalyptic number.

21071663 is a deficient number, since it is larger than the sum of its proper divisors (513985).

21071663 is an equidigital number, since it uses as much as digits as its factorization.

21071663 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 513984.

The product of its (nonzero) digits is 1512, while the sum is 26.

The square root of 21071663 is about 4590.3881099532. The cubic root of 21071663 is about 276.2058911441.

Adding to 21071663 its reverse (36617012), we get a palindrome (57688675).

The spelling of 21071663 in words is "twenty-one million, seventy-one thousand, six hundred sixty-three".