66681561 has 4 divisors (see below), whose sum is σ = 88908752. Its totient is φ = 44454372.

The previous prime is 66681547. The next prime is 66681607. The reversal of 66681561 is 16518666.

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.

It is a de Polignac number, because none of the positive numbers 2^k-66681561 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (66681521) 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, 11113591 + ... + 11113596.

It is an arithmetic number, because the mean of its divisors is an integer number (22227188).

Almost surely, 2^66681561 is an apocalyptic number.

It is an amenable number.

66681561 is a deficient number, since it is larger than the sum of its proper divisors (22227191).

66681561 is a wasteful number, since it uses less digits than its factorization.

66681561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 22227190.

The product of its digits is 51840, while the sum is 39.

The square root of 66681561 is about 8165.8778462576. The cubic root of 66681561 is about 405.5103275710.

The spelling of 66681561 in words is "sixty-six million, six hundred eighty-one thousand, five hundred sixty-one".