1666691665 has 32 divisors (see below), whose sum is σ = 2130739200. Its totient is φ = 1248882624.

The previous prime is 1666691659. The next prime is 1666691671. The reversal of 1666691665 is 5661966661.

It is an interprime number because it is at equal distance from previous prime (1666691659) and next prime (1666691671).

It is a cyclic number.

It is not a de Polignac number, because 1666691665 - 2¹¹ = 1666689617 is a prime.

It is a super-2 number, since 2×1666691665² = 5555722212360944450, which contains 22 as substring.

It is an unprimeable number.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 1532752 + ... + 1533838.

It is an arithmetic number, because the mean of its divisors is an integer number (66585600).

Almost surely, 2^1666691665 is an apocalyptic number.

It is an amenable number.

1666691665 is a deficient number, since it is larger than the sum of its proper divisors (464047535).

1666691665 is a wasteful number, since it uses less digits than its factorization.

1666691665 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1381.

The product of its digits is 2099520, while the sum is 52.

The square root of 1666691665 is about 40825.1352110437. The cubic root of 1666691665 is about 1185.6370292273.

The spelling of 1666691665 in words is "one billion, six hundred sixty-six million, six hundred ninety-one thousand, six hundred sixty-five".