21018890 has 16 divisors (see below), whose sum is σ = 38353608. Its totient is φ = 8292096.

The previous prime is 21018869. The next prime is 21018929. The reversal of 21018890 is 9881012.

It can be written as a sum of positive squares in 4 ways, for example, as 15311569 + 5707321 = 3913^2 + 2389^2 .

It is a Curzon number.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 13667 + ... + 15126.

Almost surely, 2^21018890 is an apocalyptic number.

21018890 is a deficient number, since it is larger than the sum of its proper divisors (17334718).

21018890 is a wasteful number, since it uses less digits than its factorization.

21018890 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 28873.

The product of its (nonzero) digits is 1152, while the sum is 29.

The square root of 21018890 is about 4584.6362996425. The cubic root of 21018890 is about 275.9751167793.

The spelling of 21018890 in words is "twenty-one million, eighteen thousand, eight hundred ninety".