166638509 has 4 divisors (see below), whose sum is σ = 166706880. Its totient is φ = 166570140.

The previous prime is 166638499. The next prime is 166638529. The reversal of 166638509 is 905836661.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 166638509 - 2²⁴ = 149861293 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 166638509.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (166638529) 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, 30389 + ... + 35450.

It is an arithmetic number, because the mean of its divisors is an integer number (41676720).

Almost surely, 2^166638509 is an apocalyptic number.

It is an amenable number.

166638509 is a deficient number, since it is larger than the sum of its proper divisors (68371).

166638509 is an equidigital number, since it uses as much as digits as its factorization.

166638509 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 68370.

The product of its (nonzero) digits is 233280, while the sum is 44.

The square root of 166638509 is about 12908.8538995528. The cubic root of 166638509 is about 550.2902148814.

The spelling of 166638509 in words is "one hundred sixty-six million, six hundred thirty-eight thousand, five hundred nine".