661395561 has 8 divisors (see below), whose sum is σ = 882669024. Its totient is φ = 440526240.

The previous prime is 661395517. The next prime is 661395563. The reversal of 661395561 is 165593166.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 661395561 - 2¹⁹ = 660871273 is a prime.

It is a super-2 number, since 2×661395561² = 874888176221009442, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (661395563) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 97195 + ... + 103776.

It is an arithmetic number, because the mean of its divisors is an integer number (110333628).

Almost surely, 2^661395561 is an apocalyptic number.

It is an amenable number.

661395561 is a deficient number, since it is larger than the sum of its proper divisors (221273463).

661395561 is a wasteful number, since it uses less digits than its factorization.

661395561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 202071.

The product of its digits is 145800, while the sum is 42.

The square root of 661395561 is about 25717.6118836878. The cubic root of 661395561 is about 871.2720024606.

The spelling of 661395561 in words is "six hundred sixty-one million, three hundred ninety-five thousand, five hundred sixty-one".