21516518 has 4 divisors (see below), whose sum is σ = 32274780. Its totient is φ = 10758258.

The previous prime is 21516487. The next prime is 21516527. The reversal of 21516518 is 81561512.

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

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 5379128 + ... + 5379131.

It is an arithmetic number, because the mean of its divisors is an integer number (8068695).

Almost surely, 2^21516518 is an apocalyptic number.

21516518 is a deficient number, since it is larger than the sum of its proper divisors (10758262).

21516518 is a wasteful number, since it uses less digits than its factorization.

21516518 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 10758261.

The product of its digits is 2400, while the sum is 29.

The square root of 21516518 is about 4638.5900875158. The cubic root of 21516518 is about 278.1360805752.

The spelling of 21516518 in words is "twenty-one million, five hundred sixteen thousand, five hundred eighteen".