661809993 has 16 divisors (see below), whose sum is σ = 968224320. Its totient is φ = 399582144.

The previous prime is 661809991. The next prime is 661810001. The reversal of 661809993 is 399908166.

It is not a de Polignac number, because 661809993 - 2¹ = 661809991 is a prime.

It is not an unprimeable number, because it can be changed into a prime (661809991) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 158023 + ... + 162156.

It is an arithmetic number, because the mean of its divisors is an integer number (60514020).

Almost surely, 2^661809993 is an apocalyptic number.

It is an amenable number.

661809993 is a deficient number, since it is larger than the sum of its proper divisors (306414327).

661809993 is a wasteful number, since it uses less digits than its factorization.

661809993 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 320248.

The product of its (nonzero) digits is 629856, while the sum is 51.

The square root of 661809993 is about 25725.6679796658. The cubic root of 661809993 is about 871.4539448199.

The spelling of 661809993 in words is "six hundred sixty-one million, eight hundred nine thousand, nine hundred ninety-three".