66777561 has 32 divisors (see below), whose sum is σ = 102211200. Its totient is φ = 43061760.

The previous prime is 66777551. The next prime is 66777577. The reversal of 66777561 is 16577766.

It is not a de Polignac number, because 66777561 - 2⁶ = 66777497 is a prime.

It is a super-3 number, since 3×66777561³ (a number of 24 digits) contains 333 as substring.

It is not an unprimeable number, because it can be changed into a prime (66777511) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 197985 + ... + 198321.

It is an arithmetic number, because the mean of its divisors is an integer number (3194100).

Almost surely, 2^66777561 is an apocalyptic number.

It is an amenable number.

66777561 is a deficient number, since it is larger than the sum of its proper divisors (35433639).

66777561 is a wasteful number, since it uses less digits than its factorization.

66777561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 566 (or 560 counting only the distinct ones).

The product of its digits is 370440, while the sum is 45.

The square root of 66777561 is about 8171.7538509184. The cubic root of 66777561 is about 405.7048357381.

The spelling of 66777561 in words is "sixty-six million, seven hundred seventy-seven thousand, five hundred sixty-one".