21018405 has 16 divisors (see below), whose sum is σ = 34539264. Its totient is φ = 10906560.

The previous prime is 21018401. The next prime is 21018407. The reversal of 21018405 is 50481012.

It is not a de Polignac number, because 21018405 - 2² = 21018401 is a prime.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21018401) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 18381 + ... + 19490.

It is an arithmetic number, because the mean of its divisors is an integer number (2158704).

Almost surely, 2^21018405 is an apocalyptic number.

It is an amenable number.

21018405 is a deficient number, since it is larger than the sum of its proper divisors (13520859).

21018405 is a wasteful number, since it uses less digits than its factorization.

21018405 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 37916.

The product of its (nonzero) digits is 320, while the sum is 21.

The square root of 21018405 is about 4584.5834052834. The cubic root of 21018405 is about 275.9729941020.

Adding to 21018405 its reverse (50481012), we get a palindrome (71499417).

The spelling of 21018405 in words is "twenty-one million, eighteen thousand, four hundred five".