66123781 has 16 divisors (see below), whose sum is σ = 73008000. Its totient is φ = 59609088.

The previous prime is 66123779. The next prime is 66123803. The reversal of 66123781 is 18732166.

66123781 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a cyclic number.

It is not a de Polignac number, because 66123781 - 2¹ = 66123779 is a prime.

It is a super-2 number, since 2×66123781² = 8744708827471922, 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 (66123581) 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 15 ways as a sum of consecutive naturals, for example, 147045 + ... + 147493.

It is an arithmetic number, because the mean of its divisors is an integer number (4563000).

Almost surely, 2^66123781 is an apocalyptic number.

It is an amenable number.

66123781 is a deficient number, since it is larger than the sum of its proper divisors (6884219).

66123781 is a wasteful number, since it uses less digits than its factorization.

66123781 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 828.

The product of its digits is 12096, while the sum is 34.

The square root of 66123781 is about 8131.6530299811. The cubic root of 66123781 is about 404.3764850598.

It can be divided in two parts, 661 and 23781, that added together give a palindrome (24442).

The spelling of 66123781 in words is "sixty-six million, one hundred twenty-three thousand, seven hundred eighty-one".