18071521 has 4 divisors (see below), whose sum is σ = 19461652. Its totient is φ = 16681392.

The previous prime is 18071509. The next prime is 18071549. The reversal of 18071521 is 12517081.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 1782225 + 16289296 = 1335^2 + 4036^2 .

It is not a de Polignac number, because 18071521 - 2⁷ = 18071393 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (18071591) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 695046 + ... + 695071.

It is an arithmetic number, because the mean of its divisors is an integer number (4865413).

Almost surely, 2^18071521 is an apocalyptic number.

It is an amenable number.

18071521 is a deficient number, since it is larger than the sum of its proper divisors (1390131).

18071521 is a wasteful number, since it uses less digits than its factorization.

18071521 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1390130.

The product of its (nonzero) digits is 560, while the sum is 25.

The square root of 18071521 is about 4251.0611616395. The cubic root of 18071521 is about 262.4207881932.

The spelling of 18071521 in words is "eighteen million, seventy-one thousand, five hundred twenty-one".