1664545661 has 4 divisors (see below), whose sum is σ = 1684600512. Its totient is φ = 1644490812.

The previous prime is 1664545657. The next prime is 1664545679. The reversal of 1664545661 is 1665454661.

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: 1665454661 = 13 ⋅128111897.

It is a cyclic number.

It is not a de Polignac number, because 1664545661 - 2² = 1664545657 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1664545601) 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, 10027301 + ... + 10027466.

It is an arithmetic number, because the mean of its divisors is an integer number (421150128).

Almost surely, 2^1664545661 is an apocalyptic number.

It is an amenable number.

1664545661 is a deficient number, since it is larger than the sum of its proper divisors (20054851).

1664545661 is an equidigital number, since it uses as much as digits as its factorization.

1664545661 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 20054850.

The product of its digits is 518400, while the sum is 44.

The square root of 1664545661 is about 40798.8438684235. The cubic root of 1664545661 is about 1185.1279419385.

The spelling of 1664545661 in words is "one billion, six hundred sixty-four million, five hundred forty-five thousand, six hundred sixty-one".