66666981 has 4 divisors (see below), whose sum is σ = 88889312. Its totient is φ = 44444652.

The previous prime is 66666973. The next prime is 66666983. The reversal of 66666981 is 18966666.

It is a happy number.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is not a de Polignac number, because 66666981 - 2³ = 66666973 is a prime.

It is a super-2 number, since 2×66666981² = 8888972711308722, 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 66666981.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (66666983) 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, 11111161 + ... + 11111166.

It is an arithmetic number, because the mean of its divisors is an integer number (22222328).

Almost surely, 2^66666981 is an apocalyptic number.

It is an amenable number.

66666981 is a deficient number, since it is larger than the sum of its proper divisors (22222331).

66666981 is a wasteful number, since it uses less digits than its factorization.

66666981 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 22222330.

The product of its digits is 559872, while the sum is 48.

The square root of 66666981 is about 8164.9850581615. The cubic root of 66666981 is about 405.4807703168.

The spelling of 66666981 in words is "sixty-six million, six hundred sixty-six thousand, nine hundred eighty-one".