21516023 has 4 divisors (see below), whose sum is σ = 21547080. Its totient is φ = 21484968.

The previous prime is 21515983. The next prime is 21516029. The reversal of 21516023 is 32061512.

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 21516023 - 2¹² = 21511927 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21515986 and 21516004.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21516029) 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, 14465 + ... + 15882.

It is an arithmetic number, because the mean of its divisors is an integer number (5386770).

Almost surely, 2^21516023 is an apocalyptic number.

21516023 is a deficient number, since it is larger than the sum of its proper divisors (31057).

21516023 is an equidigital number, since it uses as much as digits as its factorization.

21516023 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 31056.

The product of its (nonzero) digits is 360, while the sum is 20.

The square root of 21516023 is about 4638.5367304787. The cubic root of 21516023 is about 278.1339476648.

Adding to 21516023 its reverse (32061512), we get a palindrome (53577535).

The spelling of 21516023 in words is "twenty-one million, five hundred sixteen thousand, twenty-three".