66240781 has 4 divisors (see below), whose sum is σ = 66685500. Its totient is φ = 65796064.

The previous prime is 66240761. The next prime is 66240791. The reversal of 66240781 is 18704266.

66240781 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

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 25918281 + 40322500 = 5091^2 + 6350^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-66240781 is a prime.

It is a super-2 number, since 2×66240781² = 8775682134979922, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (66240701) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 222136 + ... + 222433.

It is an arithmetic number, because the mean of its divisors is an integer number (16671375).

Almost surely, 2^66240781 is an apocalyptic number.

It is an amenable number.

66240781 is a deficient number, since it is larger than the sum of its proper divisors (444719).

66240781 is a wasteful number, since it uses less digits than its factorization.

66240781 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 444718.

The product of its (nonzero) digits is 16128, while the sum is 34.

The square root of 66240781 is about 8138.8439596788. The cubic root of 66240781 is about 404.6148469655.

The spelling of 66240781 in words is "sixty-six million, two hundred forty thousand, seven hundred eighty-one".