21218415 has 16 divisors (see below), whose sum is σ = 35045376. Its totient is φ = 10951200.

The previous prime is 21218413. The next prime is 21218419. The reversal of 21218415 is 51481212.

It is not a de Polignac number, because 21218415 - 2¹ = 21218413 is a prime.

It is a super-2 number, since 2×21218415² = 900442270224450, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21218413) by changing a digit.

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 15 ways as a sum of consecutive naturals, for example, 22351 + ... + 23280.

It is an arithmetic number, because the mean of its divisors is an integer number (2190336).

Almost surely, 2^21218415 is an apocalyptic number.

21218415 is a deficient number, since it is larger than the sum of its proper divisors (13826961).

21218415 is a wasteful number, since it uses less digits than its factorization.

21218415 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 45670.

The product of its digits is 640, while the sum is 24.

The square root of 21218415 is about 4606.3450804298. The cubic root of 21218415 is about 276.8456133343.

Adding to 21218415 its reverse (51481212), we get a palindrome (72699627).

The spelling of 21218415 in words is "twenty-one million, two hundred eighteen thousand, four hundred fifteen".