66461561 has 4 divisors (see below), whose sum is σ = 66708900. Its totient is φ = 66214224.

The previous prime is 66461557. The next prime is 66461581. The reversal of 66461561 is 16516466.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 16516466 = 2 ⋅8258233.

It can be written as a sum of positive squares in 2 ways, for example, as 11182336 + 55279225 = 3344^2 + 7435^2 .

It is a cyclic number.

It is not a de Polignac number, because 66461561 - 2² = 66461557 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (66461581) 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, 123266 + ... + 123803.

It is an arithmetic number, because the mean of its divisors is an integer number (16677225).

Almost surely, 2^66461561 is an apocalyptic number.

It is an amenable number.

66461561 is a deficient number, since it is larger than the sum of its proper divisors (247339).

66461561 is a wasteful number, since it uses less digits than its factorization.

66461561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 247338.

The product of its digits is 25920, while the sum is 35.

The square root of 66461561 is about 8152.3960281625. The cubic root of 66461561 is about 405.0638744960.

The spelling of 66461561 in words is "sixty-six million, four hundred sixty-one thousand, five hundred sixty-one".