66777721 has 8 divisors (see below), whose sum is σ = 68252544. Its totient is φ = 65310960.

The previous prime is 66777713. The next prime is 66777779. The reversal of 66777721 is 12777766.

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 66777721 - 2³ = 66777713 is a prime.

It is a super-3 number, since 3×66777721³ (a number of 24 digits) contains 333 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (66777521) 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, 16576 + ... + 20206.

It is an arithmetic number, because the mean of its divisors is an integer number (8531568).

Almost surely, 2^66777721 is an apocalyptic number.

It is an amenable number.

66777721 is a deficient number, since it is larger than the sum of its proper divisors (1474823).

66777721 is a wasteful number, since it uses less digits than its factorization.

66777721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4031.

The product of its digits is 172872, while the sum is 43.

The square root of 66777721 is about 8171.7636407326. The cubic root of 66777721 is about 405.7051597628.

The spelling of 66777721 in words is "sixty-six million, seven hundred seventy-seven thousand, seven hundred twenty-one".