21518289 has 12 divisors (see below), whose sum is σ = 33473076. Its totient is φ = 13241952.

The previous prime is 21518281. The next prime is 21518333. The reversal of 21518289 is 98281512.

It can be written as a sum of positive squares in 2 ways, for example, as 1937664 + 19580625 = 1392^2 + 4425^2 .

It is not a de Polignac number, because 21518289 - 2³ = 21518281 is a prime.

It is a super-2 number, since 2×21518289² = 926073522975042, which contains 22 as substring.

It is a hoax number, since the sum of its digits (36) coincides with the sum of the digits of its distinct prime factors.

It is not an unprimeable number, because it can be changed into a prime (21518281) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 91842 + ... + 92075.

It is an arithmetic number, because the mean of its divisors is an integer number (2789423).

Almost surely, 2^21518289 is an apocalyptic number.

It is an amenable number.

21518289 is a deficient number, since it is larger than the sum of its proper divisors (11954787).

21518289 is a wasteful number, since it uses less digits than its factorization.

21518289 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 183936 (or 183933 counting only the distinct ones).

The product of its digits is 11520, while the sum is 36.

The square root of 21518289 is about 4638.7809821116. The cubic root of 21518289 is about 278.1437113868.

It can be divided in two parts, 2151 and 8289, that added together give a triangular number (10440 = T₁₄₄).

The spelling of 21518289 in words is "twenty-one million, five hundred eighteen thousand, two hundred eighty-nine".