16531561 has 4 divisors (see below), whose sum is σ = 16677972. Its totient is φ = 16385152.

The previous prime is 16531553. The next prime is 16531573. The reversal of 16531561 is 16513561.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 16513561 = 241 ⋅68521.

It can be written as a sum of positive squares in 2 ways, for example, as 571536 + 15960025 = 756^2 + 3995^2 .

It is a cyclic number.

It is not a de Polignac number, because 16531561 - 2³ = 16531553 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (16531261) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 73036 + ... + 73261.

It is an arithmetic number, because the mean of its divisors is an integer number (4169493).

Almost surely, 2^16531561 is an apocalyptic number.

It is an amenable number.

16531561 is a deficient number, since it is larger than the sum of its proper divisors (146411).

16531561 is a wasteful number, since it uses less digits than its factorization.

16531561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 146410.

The product of its digits is 2700, while the sum is 28.

The square root of 16531561 is about 4065.9022368965. The cubic root of 16531561 is about 254.7443856599.

The spelling of 16531561 in words is "sixteen million, five hundred thirty-one thousand, five hundred sixty-one".