1666620665 has 8 divisors (see below), whose sum is σ = 2005612488. Its totient is φ = 1329518080.

The previous prime is 1666620647. The next prime is 1666620671. The reversal of 1666620665 is 5660266661.

It can be written as a sum of positive squares in 4 ways, for example, as 87909376 + 1578711289 = 9376^2 + 39733^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 1666620665 - 2¹⁰ = 1666619641 is a prime.

It is a Duffinian number.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 470366 + ... + 473895.

It is an arithmetic number, because the mean of its divisors is an integer number (250701561).

Almost surely, 2^1666620665 is an apocalyptic number.

It is an amenable number.

1666620665 is a deficient number, since it is larger than the sum of its proper divisors (338991823).

1666620665 is an equidigital number, since it uses as much as digits as its factorization.

1666620665 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 944619.

The product of its (nonzero) digits is 466560, while the sum is 44.

The square root of 1666620665 is about 40824.2656394454. The cubic root of 1666620665 is about 1185.6201931950.

The spelling of 1666620665 in words is "one billion, six hundred sixty-six million, six hundred twenty thousand, six hundred sixty-five".