1666699991 has 16 divisors (see below), whose sum is σ = 1901276928. Its totient is φ = 1446244800.

The previous prime is 1666699987. The next prime is 1666699997. The reversal of 1666699991 is 1999966661.

It is not a de Polignac number, because 1666699991 - 2² = 1666699987 is a prime.

1666699991 is a strobogrammatic number because it is the same when read upside-down.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1666699997) by changing a digit.

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, 117515 + ... + 130931.

It is an arithmetic number, because the mean of its divisors is an integer number (118829808).

Almost surely, 2^1666699991 is an apocalyptic number.

1666699991 is a gapful number since it is divisible by the number (11) formed by its first and last digit.

1666699991 is a deficient number, since it is larger than the sum of its proper divisors (234576937).

1666699991 is a wasteful number, since it uses less digits than its factorization.

1666699991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 13942.

The product of its digits is 8503056, while the sum is 62.

The square root of 1666699991 is about 40825.2371824096. The cubic root of 1666699991 is about 1185.6390035172.

The spelling of 1666699991 in words is "one billion, six hundred sixty-six million, six hundred ninety-nine thousand, nine hundred ninety-one".