66643781 has 8 divisors (see below), whose sum is σ = 68400384. Its totient is φ = 64908720.

The previous prime is 66643777. The next prime is 66643783. The reversal of 66643781 is 18734666.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 66643781 - 2² = 66643777 is a prime.

It is a super-2 number, since 2×66643781² = 8882787091951922, which contains 22 as substring.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (66643783) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 980 + ... + 11586.

It is an arithmetic number, because the mean of its divisors is an integer number (8550048).

Almost surely, 2^66643781 is an apocalyptic number.

66643781 is a gapful number since it is divisible by the number (61) formed by its first and last digit.

It is an amenable number.

66643781 is a deficient number, since it is larger than the sum of its proper divisors (1756603).

66643781 is a wasteful number, since it uses less digits than its factorization.

66643781 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 10771.

The product of its digits is 145152, while the sum is 41.

The square root of 66643781 is about 8163.5642338381. The cubic root of 66643781 is about 405.4337293121.

The spelling of 66643781 in words is "sixty-six million, six hundred forty-three thousand, seven hundred eighty-one".