66361681 has 4 divisors (see below), whose sum is σ = 66651700. Its totient is φ = 66071664.

The previous prime is 66361663. The next prime is 66361709. The reversal of 66361681 is 18616366.

It is a happy number.

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 55577025 + 10784656 = 7455^2 + 3284^2 .

It is a cyclic number.

It is not a de Polignac number, because 66361681 - 2⁵ = 66361649 is a prime.

It is a super-2 number, since 2×66361681² = 8807745410291522, which contains 22 as substring.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 66361681.

It is not an unprimeable number, because it can be changed into a prime (66361621) 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, 144666 + ... + 145123.

It is an arithmetic number, because the mean of its divisors is an integer number (16662925).

Almost surely, 2^66361681 is an apocalyptic number.

It is an amenable number.

66361681 is a deficient number, since it is larger than the sum of its proper divisors (290019).

66361681 is a wasteful number, since it uses less digits than its factorization.

66361681 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 290018.

The product of its digits is 31104, while the sum is 37.

The square root of 66361681 is about 8146.2679185011. The cubic root of 66361681 is about 404.8608595849.

It can be divided in two parts, 663616 and 81, that multiplied together give a triangular number (53752896 = T₁₀₃₆₈).

The spelling of 66361681 in words is "sixty-six million, three hundred sixty-one thousand, six hundred eighty-one".