661622561 has 2 divisors, whose sum is σ = 661622562. Its totient is φ = 661622560.

The previous prime is 661622543. The next prime is 661622569. The reversal of 661622561 is 165226166.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 656128225 + 5494336 = 25615^2 + 2344^2 .

It is a cyclic number.

It is not a de Polignac number, because 661622561 - 2¹⁴ = 661606177 is a prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (661622569) 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, 330811280 + 330811281.

It is an arithmetic number, because the mean of its divisors is an integer number (330811281).

Almost surely, 2^661622561 is an apocalyptic number.

It is an amenable number.

661622561 is a deficient number, since it is larger than the sum of its proper divisors (1).

661622561 is an equidigital number, since it uses as much as digits as its factorization.

661622561 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 25920, while the sum is 35.

The square root of 661622561 is about 25722.0248230966. The cubic root of 661622561 is about 871.3716685474.

The spelling of 661622561 in words is "six hundred sixty-one million, six hundred twenty-two thousand, five hundred sixty-one".