1666501561 has 8 divisors (see below), whose sum is σ = 1677259080. Its totient is φ = 1655757312.

The previous prime is 1666501553. The next prime is 1666501579. The reversal of 1666501561 is 1651056661.

It can be written as a sum of positive squares in 4 ways, for example, as 499254336 + 1167247225 = 22344^2 + 34165^2 .

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

It is a cyclic number.

It is not a de Polignac number, because 1666501561 - 2³ = 1666501553 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 1666501561.

It is not an unprimeable number, because it can be changed into a prime (1666501531) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 401545 + ... + 405673.

It is an arithmetic number, because the mean of its divisors is an integer number (209657385).

Almost surely, 2^1666501561 is an apocalyptic number.

It is an amenable number.

1666501561 is a deficient number, since it is larger than the sum of its proper divisors (10757519).

1666501561 is a wasteful number, since it uses less digits than its factorization.

1666501561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 6635.

The product of its (nonzero) digits is 32400, while the sum is 37.

The square root of 1666501561 is about 40822.8068731193. The cubic root of 1666501561 is about 1185.5919493211.

Subtracting from 1666501561 its reverse (1651056661), we obtain a square (15444900 = 3930²).

The spelling of 1666501561 in words is "one billion, six hundred sixty-six million, five hundred one thousand, five hundred sixty-one".