661185275689 has 3 divisors (see below), whose sum is σ = 661186088823. Its totient is φ = 661184462556.

The previous prime is 661185275683. The next prime is 661185275759. The reversal of 661185275689 is 986572581166.

The square root of 661185275689 is 813133.

It is a perfect power (a square), and thus also a powerful number.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It can be written as a sum of positive squares in only one way, i.e., 349700736025 + 311484539664 = 591355^2 + 558108^2 .

It is not a de Polignac number, because 661185275689 - 2⁵ = 661185275657 is a prime.

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 661185275689.

It is not an unprimeable number, because it can be changed into a prime (661185275683) by changing a digit.

It is a polite number, since it can be written in 2 ways as a sum of consecutive naturals, for example, 406567 + ... + 1219699.

It is an arithmetic number, because the mean of its divisors is an integer number (220395362941).

Almost surely, 2^661185275689 is an apocalyptic number.

661185275689 is the 813133-rd square number.

661185275689 is the 406567-th centered octagonal number.

It is an amenable number.

661185275689 is a deficient number, since it is larger than the sum of its proper divisors (813134).

661185275689 is an frugal number, since it uses more digits than its factorization.

661185275689 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1626266 (or 813133 counting only the distinct ones).

The product of its digits is 43545600, while the sum is 64.

Multiplying 661185275689 by its sum of digits (64), we get a square (42315857644096 = 6505064²).

The spelling of 661185275689 in words is "six hundred sixty-one billion, one hundred eighty-five million, two hundred seventy-five thousand, six hundred eighty-nine".