21518138 has 8 divisors (see below), whose sum is σ = 32563188. Its totient is φ = 10663744.

The previous prime is 21518131. The next prime is 21518143. The reversal of 21518138 is 83181512.

It can be written as a sum of positive squares in 2 ways, for example, as 16752649 + 4765489 = 4093^2 + 2183^2 .

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

It is a self number, because there is not a number n which added to its sum of digits gives 21518138.

It is not an unprimeable number, because it can be changed into a prime (21518131) 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, 47381 + ... + 47832.

Almost surely, 2^21518138 is an apocalyptic number.

21518138 is a deficient number, since it is larger than the sum of its proper divisors (11045050).

21518138 is a wasteful number, since it uses less digits than its factorization.

21518138 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 95328.

The product of its digits is 1920, while the sum is 29.

The square root of 21518138 is about 4638.7647062553. The cubic root of 21518138 is about 278.1430607806.

The spelling of 21518138 in words is "twenty-one million, five hundred eighteen thousand, one hundred thirty-eight".