1665778775661 has 144 divisors (see below), whose sum is σ = 3265602412800. Its totient is φ = 796191897600.

The previous prime is 1665778775621. The next prime is 1665778775663.

1665778775661 is a `hidden beast` number, since 1 + 6 + 6 + 57 + 7 + 8 + 7 + 7 + 566 + 1 = 666.

1665778775661 is nontrivially palindromic in base 10.

It is not a de Polignac number, because 1665778775661 - 2²⁷ = 1665644557933 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 1665778775661.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1665778775663) by changing a digit.

It is a polite number, since it can be written in 143 ways as a sum of consecutive naturals, for example, 30792765 + ... + 30846813.

Almost surely, 2^{1665778775661} is an apocalyptic number.

1665778775661 is a gapful number since it is divisible by the number (11) formed by its first and last digit.

It is an amenable number.

1665778775661 is a deficient number, since it is larger than the sum of its proper divisors (1599823637139).

1665778775661 is a wasteful number, since it uses less digits than its factorization.

1665778775661 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 54408 (or 54394 counting only the distinct ones).

The product of its digits is 622339200, while the sum is 72.

The spelling of 1665778775661 in words is "one trillion, six hundred sixty-five billion, seven hundred seventy-eight million, seven hundred seventy-five thousand, six hundred sixty-one".