661501565 has 4 divisors (see below), whose sum is σ = 793801884. Its totient is φ = 529201248.

The previous prime is 661501553. The next prime is 661501573. The reversal of 661501565 is 565105166.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 565105166 = 2 ⋅282552583.

It can be written as a sum of positive squares in 2 ways, for example, as 451222564 + 210279001 = 21242^2 + 14501^2 .

It is a cyclic number.

It is not a de Polignac number, because 661501565 - 2¹⁸ = 661239421 is a prime.

It is a Duffinian number.

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, 66150152 + ... + 66150161.

It is an arithmetic number, because the mean of its divisors is an integer number (198450471).

Almost surely, 2^661501565 is an apocalyptic number.

It is an amenable number.

661501565 is a deficient number, since it is larger than the sum of its proper divisors (132300319).

661501565 is a wasteful number, since it uses less digits than its factorization.

661501565 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 132300318.

The product of its (nonzero) digits is 27000, while the sum is 35.

The square root of 661501565 is about 25719.6727234232. The cubic root of 661501565 is about 871.3185471655.

The spelling of 661501565 in words is "six hundred sixty-one million, five hundred one thousand, five hundred sixty-five".