21018505 has 8 divisors (see below), whose sum is σ = 25526592. Its totient is φ = 16611888.

The previous prime is 21018499. The next prime is 21018509. The reversal of 21018505 is 50581012.

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 21018505 - 2³ = 21018497 is a prime.

It is an alternating number because its digits alternate between even and odd.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21018509) 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 7 ways as a sum of consecutive naturals, for example, 24909 + ... + 25738.

It is an arithmetic number, because the mean of its divisors is an integer number (3190824).

Almost surely, 2^21018505 is an apocalyptic number.

It is an amenable number.

21018505 is a deficient number, since it is larger than the sum of its proper divisors (4508087).

21018505 is an equidigital number, since it uses as much as digits as its factorization.

21018505 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 50735.

The product of its (nonzero) digits is 400, while the sum is 22.

The square root of 21018505 is about 4584.5943113868. The cubic root of 21018505 is about 275.9734317701.

Adding to 21018505 its reverse (50581012), we get a palindrome (71599517).

The spelling of 21018505 in words is "twenty-one million, eighteen thousand, five hundred five".