21518506 has 8 divisors (see below), whose sum is σ = 32388804. Its totient is φ = 10722240.

The previous prime is 21518503. The next prime is 21518521. The reversal of 21518506 is 60581512.

It can be written as a sum of positive squares in 2 ways, for example, as 21242881 + 275625 = 4609^2 + 525^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is a super-2 number, since 2×21518506² = 926092200944072, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (21518503) 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, 17775 + ... + 18946.

Almost surely, 2^21518506 is an apocalyptic number.

21518506 is a deficient number, since it is larger than the sum of its proper divisors (10870298).

21518506 is a wasteful number, since it uses less digits than its factorization.

21518506 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 37016.

The product of its (nonzero) digits is 2400, while the sum is 28.

The square root of 21518506 is about 4638.8043718182. The cubic root of 21518506 is about 278.1446463587.

It can be divided in two parts, 215 and 18506, that added together give a triangular number (18721 = T₁₉₃).

The spelling of 21518506 in words is "twenty-one million, five hundred eighteen thousand, five hundred six".