661744645 has 4 divisors (see below), whose sum is σ = 794093580. Its totient is φ = 529395712.

The previous prime is 661744621. The next prime is 661744679. The reversal of 661744645 is 546447166.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 546447166 = 2 ⋅273223583.

It can be written as a sum of positive squares in 2 ways, for example, as 190246849 + 471497796 = 13793^2 + 21714^2 .

It is a cyclic number.

It is not a de Polignac number, because 661744645 - 2¹⁵ = 661711877 is a prime.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 66174460 + ... + 66174469.

It is an arithmetic number, because the mean of its divisors is an integer number (198523395).

Almost surely, 2^661744645 is an apocalyptic number.

It is an amenable number.

661744645 is a deficient number, since it is larger than the sum of its proper divisors (132348935).

661744645 is a wasteful number, since it uses less digits than its factorization.

661744645 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 132348934.

The product of its digits is 483840, while the sum is 43.

The square root of 661744645 is about 25724.3978549547. The cubic root of 661744645 is about 871.4252610348.

The spelling of 661744645 in words is "six hundred sixty-one million, seven hundred forty-four thousand, six hundred forty-five".