661561601 has 8 divisors (see below), whose sum is σ = 684731880. Its totient is φ = 638415232.

The previous prime is 661561583. The next prime is 661561651. The reversal of 661561601 is 106165166.

It can be written as a sum of positive squares in 4 ways, for example, as 6150400 + 655411201 = 2480^2 + 25601^2 .

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

It is a cyclic number.

It is not a de Polignac number, because 661561601 - 2¹⁴ = 661545217 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (661561651) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 64631 + ... + 74163.

It is an arithmetic number, because the mean of its divisors is an integer number (85591485).

Almost surely, 2^661561601 is an apocalyptic number.

It is an amenable number.

661561601 is a deficient number, since it is larger than the sum of its proper divisors (23170279).

661561601 is a wasteful number, since it uses less digits than its factorization.

661561601 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 11955.

The product of its (nonzero) digits is 6480, while the sum is 32.

The square root of 661561601 is about 25720.8398191039. The cubic root of 661561601 is about 871.3449058322.

The spelling of 661561601 in words is "six hundred sixty-one million, five hundred sixty-one thousand, six hundred one".