21518811 has 16 divisors (see below), whose sum is σ = 33558400. Its totient is φ = 13590504.

The previous prime is 21518807. The next prime is 21518813. The reversal of 21518811 is 11881512.

It is not a de Polignac number, because 21518811 - 2² = 21518807 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21518813) 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, 20461 + ... + 21486.

It is an arithmetic number, because the mean of its divisors is an integer number (2097400).

Almost surely, 2^21518811 is an apocalyptic number.

21518811 is a deficient number, since it is larger than the sum of its proper divisors (12039589).

21518811 is a wasteful number, since it uses less digits than its factorization.

21518811 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 41975 (or 41969 counting only the distinct ones).

The product of its digits is 640, while the sum is 27.

The square root of 21518811 is about 4638.8372465522. The cubic root of 21518811 is about 278.1459604790.

The spelling of 21518811 in words is "twenty-one million, five hundred eighteen thousand, eight hundred eleven".