100561 has 4 divisors (see below), whose sum is σ = 101232. Its totient is φ = 99892.

The previous prime is 100559. The next prime is 100591. The reversal of 100561 is 165001.

100561 is nontrivially palindromic in base 15.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also a brilliant number, because the two primes have the same length.

It is a cyclic number.

It is not a de Polignac number, because 100561 - 2¹ = 100559 is a prime.

It is a super-2 number, since 2×100561² = 20225029442, which contains 22 as substring.

It is an Ulam number.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (100501) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 6 + ... + 448.

It is an arithmetic number, because the mean of its divisors is an integer number (25308).

2¹⁰⁰⁵⁶¹ is an apocalyptic number.

It is an amenable number.

100561 is a deficient number, since it is larger than the sum of its proper divisors (671).

100561 is an equidigital number, since it uses as much as digits as its factorization.

100561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 670.

The product of its (nonzero) digits is 30, while the sum is 13.

The square root of 100561 is about 317.1135443339. The cubic root of 100561 is about 46.5025242396.

Adding to 100561 its reverse (165001), we get a palindrome (265562).

The spelling of 100561 in words is "one hundred thousand, five hundred sixty-one".