1665755661 has 4 divisors (see below), whose sum is σ = 2221007552. Its totient is φ = 1110503772.

The previous prime is 1665755653. The next prime is 1665755677. The reversal of 1665755661 is 1665575661.

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, and also an emirpimes, since its reverse is a distinct semiprime: 1665575661 = 3 ⋅555191887.

It is not a de Polignac number, because 1665755661 - 2³ = 1665755653 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 1665755661.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1665755681) 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, 277625941 + ... + 277625946.

It is an arithmetic number, because the mean of its divisors is an integer number (555251888).

Almost surely, 2^1665755661 is an apocalyptic number.

It is an amenable number.

1665755661 is a deficient number, since it is larger than the sum of its proper divisors (555251891).

1665755661 is an equidigital number, since it uses as much as digits as its factorization.

1665755661 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 555251890.

The product of its digits is 1134000, while the sum is 48.

The square root of 1665755661 is about 40813.6700261077. The cubic root of 1665755661 is about 1185.4150387946.

The spelling of 1665755661 in words is "one billion, six hundred sixty-five million, seven hundred fifty-five thousand, six hundred sixty-one".