21018550 has 72 divisors (see below), whose sum is σ = 47581776. Its totient is φ = 6874560.

The previous prime is 21018539. The next prime is 21018551. The reversal of 21018550 is 5581012.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21018551) 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 35 ways as a sum of consecutive naturals, for example, 56164 + ... + 56536.

It is an arithmetic number, because the mean of its divisors is an integer number (660858).

Almost surely, 2^21018550 is an apocalyptic number.

21018550 is an abundant number, since it is smaller than the sum of its proper divisors (26563226).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21018550 is a wasteful number, since it uses less digits than its factorization.

21018550 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 422 (or 410 counting only the distinct ones).

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

The square root of 21018550 is about 4584.5992191248. The cubic root of 21018550 is about 275.9736287203.

Adding to 21018550 its reverse (5581012), we get a palindrome (26599562).

The spelling of 21018550 in words is "twenty-one million, eighteen thousand, five hundred fifty".