21218315 has 8 divisors (see below), whose sum is σ = 25531440. Its totient is φ = 16928352.

The previous prime is 21218311. The next prime is 21218317. The reversal of 21218315 is 51381212.

It is a happy number.

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

It is a cyclic number.

It is not a de Polignac number, because 21218315 - 2² = 21218311 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21218311) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 3704 + ... + 7493.

It is an arithmetic number, because the mean of its divisors is an integer number (3191430).

Almost surely, 2^21218315 is an apocalyptic number.

21218315 is a deficient number, since it is larger than the sum of its proper divisors (4313125).

21218315 is a wasteful number, since it uses less digits than its factorization.

21218315 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 11581.

The product of its digits is 480, while the sum is 23.

The square root of 21218315 is about 4606.3342258243. The cubic root of 21218315 is about 276.8451784196.

Adding to 21218315 its reverse (51381212), we get a palindrome (72599527).

The spelling of 21218315 in words is "twenty-one million, two hundred eighteen thousand, three hundred fifteen".