1666535641 has 4 divisors (see below), whose sum is σ = 1666617984. Its totient is φ = 1666453300.

The previous prime is 1666535621. The next prime is 1666535659. The reversal of 1666535641 is 1465356661.

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 a brilliant number, because the two primes have the same length, and also an emirpimes, since its reverse is a distinct semiprime: 1465356661 = 3719 ⋅394019.

It is a cyclic number.

It is not a de Polignac number, because 1666535641 - 2⁵ = 1666535609 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (1666535621) 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, 12576 + ... + 59086.

It is an arithmetic number, because the mean of its divisors is an integer number (416654496).

Almost surely, 2^1666535641 is an apocalyptic number.

It is an amenable number.

1666535641 is a deficient number, since it is larger than the sum of its proper divisors (82343).

1666535641 is an equidigital number, since it uses as much as digits as its factorization.

1666535641 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 82342.

The product of its digits is 388800, while the sum is 43.

The square root of 1666535641 is about 40823.2242847132. The cubic root of 1666535641 is about 1185.6000310614.

The spelling of 1666535641 in words is "one billion, six hundred sixty-six million, five hundred thirty-five thousand, six hundred forty-one".