661809959 has 4 divisors (see below), whose sum is σ = 667881720. Its totient is φ = 655738200.

The previous prime is 661809937. The next prime is 661809971. The reversal of 661809959 is 959908166.

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

It is a cyclic number.

It is not a de Polignac number, because 661809959 - 2⁸ = 661809703 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 661809959.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (661809989) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3035717 + ... + 3035934.

It is an arithmetic number, because the mean of its divisors is an integer number (166970430).

Almost surely, 2^661809959 is an apocalyptic number.

661809959 is a deficient number, since it is larger than the sum of its proper divisors (6071761).

661809959 is a wasteful number, since it uses less digits than its factorization.

661809959 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 6071760.

The product of its (nonzero) digits is 1049760, while the sum is 53.

The square root of 661809959 is about 25725.6673188471. The cubic root of 661809959 is about 871.4539298964.

The spelling of 661809959 in words is "six hundred sixty-one million, eight hundred nine thousand, nine hundred fifty-nine".