166401320661 has 6 divisors (see below), whose sum is σ = 240357463190. Its totient is φ = 110934213768.

The previous prime is 166401320639. The next prime is 166401320669. The reversal of 166401320661 is 166023104661.

It is a happy number.

166401320661 is a `hidden beast` number, since 1 + 6 + 640 + 1 + 3 + 2 + 0 + 6 + 6 + 1 = 666.

It can be written as a sum of positive squares in only one way, i.e., 112342280625 + 54059040036 = 335175^2 + 232506^2 .

It is not a de Polignac number, because 166401320661 - 2¹⁷ = 166401189589 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (166401320669) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 9244517806 + ... + 9244517823.

Almost surely, 2^166401320661 is an apocalyptic number.

It is an amenable number.

166401320661 is a deficient number, since it is larger than the sum of its proper divisors (73956142529).

166401320661 is a wasteful number, since it uses less digits than its factorization.

166401320661 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 18489035635 (or 18489035632 counting only the distinct ones).

The product of its (nonzero) digits is 31104, while the sum is 36.

The spelling of 166401320661 in words is "one hundred sixty-six billion, four hundred one million, three hundred twenty thousand, six hundred sixty-one".