101666561 has 4 divisors (see below), whose sum is σ = 103584852. Its totient is φ = 99748272.

The previous prime is 101666557. The next prime is 101666563. The reversal of 101666561 is 165666101.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 165666101 = 5347 ⋅30983.

It can be written as a sum of positive squares in 2 ways, for example, as 75082225 + 26584336 = 8665^2 + 5156^2 .

It is a cyclic number.

It is not a de Polignac number, because 101666561 - 2² = 101666557 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (101666563) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 959066 + ... + 959171.

It is an arithmetic number, because the mean of its divisors is an integer number (25896213).

Almost surely, 2^101666561 is an apocalyptic number.

It is an amenable number.

101666561 is a deficient number, since it is larger than the sum of its proper divisors (1918291).

101666561 is an equidigital number, since it uses as much as digits as its factorization.

101666561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1918290.

The product of its (nonzero) digits is 6480, while the sum is 32.

The square root of 101666561 is about 10082.9837349864. The cubic root of 101666561 is about 466.7231874285.

The spelling of 101666561 in words is "one hundred one million, six hundred sixty-six thousand, five hundred sixty-one".