21131218 has 8 divisors (see below), whose sum is σ = 32553612. Its totient is φ = 10280016.

The previous prime is 21131191. The next prime is 21131251. The reversal of 21131218 is 81213112.

It can be written as a sum of positive squares in 2 ways, for example, as 20820969 + 310249 = 4563^2 + 557^2 .

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

It is a junction number, because it is equal to n+sod(n) for n = 21131195 and 21131204.

It is an unprimeable number.

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, 142705 + ... + 142852.

Almost surely, 2^21131218 is an apocalyptic number.

21131218 is a deficient number, since it is larger than the sum of its proper divisors (11422394).

21131218 is a wasteful number, since it uses less digits than its factorization.

21131218 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 285596.

The product of its digits is 96, while the sum is 19.

The square root of 21131218 is about 4596.8704571697. The cubic root of 21131218 is about 276.4658606440.

The spelling of 21131218 in words is "twenty-one million, one hundred thirty-one thousand, two hundred eighteen".