21018361 has 24 divisors (see below), whose sum is σ = 26410560. Its totient is φ = 16376256.

The previous prime is 21018323. The next prime is 21018397. The reversal of 21018361 is 16381012.

It is not a de Polignac number, because 21018361 - 2¹⁵ = 20985593 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 (21018461) 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 23 ways as a sum of consecutive naturals, for example, 128866 + ... + 129028.

It is an arithmetic number, because the mean of its divisors is an integer number (1100440).

Almost surely, 2^21018361 is an apocalyptic number.

It is an amenable number.

21018361 is a deficient number, since it is larger than the sum of its proper divisors (5392199).

21018361 is a wasteful number, since it uses less digits than its factorization.

21018361 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 305 (or 292 counting only the distinct ones).

The product of its (nonzero) digits is 288, while the sum is 22.

The square root of 21018361 is about 4584.5786065897. The cubic root of 21018361 is about 275.9728015276.

Adding to 21018361 its reverse (16381012), we get a palindrome (37399373).

The spelling of 21018361 in words is "twenty-one million, eighteen thousand, three hundred sixty-one".