21815963 has 4 divisors (see below), whose sum is σ = 23494128. Its totient is φ = 20137800.

The previous prime is 21815939. The next prime is 21815987. The reversal of 21815963 is 36951812.

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

It is an interprime number because it is at equal distance from previous prime (21815939) and next prime (21815987).

It is a cyclic number.

It is not a de Polignac number, because 21815963 - 2¹⁶ = 21750427 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21817963) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 839063 + ... + 839088.

It is an arithmetic number, because the mean of its divisors is an integer number (5873532).

Almost surely, 2^21815963 is an apocalyptic number.

21815963 is a deficient number, since it is larger than the sum of its proper divisors (1678165).

21815963 is a wasteful number, since it uses less digits than its factorization.

21815963 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1678164.

The product of its digits is 12960, while the sum is 35.

The square root of 21815963 is about 4670.7561486338. The cubic root of 21815963 is about 279.4204125021.

The spelling of 21815963 in words is "twenty-one million, eight hundred fifteen thousand, nine hundred sixty-three".