1666121665 has 16 divisors (see below), whose sum is σ = 2179090368. Its totient is φ = 1215539136.

The previous prime is 1666121657. The next prime is 1666121689. The reversal of 1666121665 is 5661216661.

It is a cyclic number.

It is not a de Polignac number, because 1666121665 - 2³ = 1666121657 is a prime.

It is a super-2 number, since 2×1666121665² = 5551922805164744450, which contains 22 as substring.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 149019 + ... + 159808.

It is an arithmetic number, because the mean of its divisors is an integer number (136193148).

Almost surely, 2^1666121665 is an apocalyptic number.

It is an amenable number.

1666121665 is a deficient number, since it is larger than the sum of its proper divisors (512968703).

1666121665 is a wasteful number, since it uses less digits than its factorization.

1666121665 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 308928.

The product of its digits is 77760, while the sum is 40.

The square root of 1666121665 is about 40818.1536206625. The cubic root of 1666121665 is about 1185.5018532223.

It can be divided in two parts, 1 and 666121665, that added together give a palindrome (666121666).

The spelling of 1666121665 in words is "one billion, six hundred sixty-six million, one hundred twenty-one thousand, six hundred sixty-five".