660778561 has 4 divisors (see below), whose sum is σ = 695556400. Its totient is φ = 626000724.

The previous prime is 660778529. The next prime is 660778571. The reversal of 660778561 is 165877066.

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 a cyclic number.

It is not a de Polignac number, because 660778561 - 2⁵ = 660778529 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (660778501) 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, 17388891 + ... + 17388928.

It is an arithmetic number, because the mean of its divisors is an integer number (173889100).

Almost surely, 2^660778561 is an apocalyptic number.

It is an amenable number.

660778561 is a deficient number, since it is larger than the sum of its proper divisors (34777839).

660778561 is a wasteful number, since it uses less digits than its factorization.

660778561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 34777838.

The product of its (nonzero) digits is 423360, while the sum is 46.

The square root of 660778561 is about 25705.6134141942. The cubic root of 660778561 is about 871.0009886088. Note that the first 3 decimals are identical.

The spelling of 660778561 in words is "six hundred sixty million, seven hundred seventy-eight thousand, five hundred sixty-one".