661600561 has 2 divisors, whose sum is σ = 661600562. Its totient is φ = 661600560.

The previous prime is 661600523. The next prime is 661600567. The reversal of 661600561 is 165006166.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 385376161 + 276224400 = 19631^2 + 16620^2 .

It is a cyclic number.

It is not a de Polignac number, because 661600561 - 2¹¹ = 661598513 is a prime.

It is not a weakly prime, because it can be changed into another prime (661600567) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 330800280 + 330800281.

It is an arithmetic number, because the mean of its divisors is an integer number (330800281).

Almost surely, 2^661600561 is an apocalyptic number.

It is an amenable number.

661600561 is a deficient number, since it is larger than the sum of its proper divisors (1).

661600561 is an equidigital number, since it uses as much as digits as its factorization.

661600561 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 6480, while the sum is 31.

The square root of 661600561 is about 25721.5971704714. The cubic root of 661600561 is about 871.3620102768.

The spelling of 661600561 in words is "six hundred sixty-one million, six hundred thousand, five hundred sixty-one".