66557681 has 4 divisors (see below), whose sum is σ = 66657252. Its totient is φ = 66458112.

The previous prime is 66557663. The next prime is 66557717. The reversal of 66557681 is 18675566.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 26615281 + 39942400 = 5159^2 + 6320^2 .

It is a cyclic number.

It is not a de Polignac number, because 66557681 - 2¹⁴ = 66541297 is a prime.

It is a super-2 number, since 2×66557681² = 8859849800195522, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (66557611) 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, 48776 + ... + 50121.

It is an arithmetic number, because the mean of its divisors is an integer number (16664313).

Almost surely, 2^66557681 is an apocalyptic number.

It is an amenable number.

66557681 is a deficient number, since it is larger than the sum of its proper divisors (99571).

66557681 is an equidigital number, since it uses as much as digits as its factorization.

66557681 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 99570.

The product of its digits is 302400, while the sum is 44.

The square root of 66557681 is about 8158.2890975988. The cubic root of 66557681 is about 405.2590549096.

The spelling of 66557681 in words is "sixty-six million, five hundred fifty-seven thousand, six hundred eighty-one".