646645561 has 2 divisors, whose sum is σ = 646645562. Its totient is φ = 646645560.

The previous prime is 646645499. The next prime is 646645579. The reversal of 646645561 is 165546646.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 522991161 + 123654400 = 22869^2 + 11120^2 .

It is a cyclic number.

It is not a de Polignac number, because 646645561 - 2⁹ = 646645049 is a prime.

It is a super-2 number, since 2×646645561² = 836300963122009442, which contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (646645591) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 323322780 + 323322781.

It is an arithmetic number, because the mean of its divisors is an integer number (323322781).

Almost surely, 2^646645561 is an apocalyptic number.

It is an amenable number.

646645561 is a deficient number, since it is larger than the sum of its proper divisors (1).

646645561 is an equidigital number, since it uses as much as digits as its factorization.

646645561 is an evil number, because the sum of its binary digits is even.

The product of its digits is 518400, while the sum is 43.

The square root of 646645561 is about 25429.2265120275. The cubic root of 646645561 is about 864.7464083376.

It can be divided in two parts, 64664 and 5561, that added together give a square (70225 = 265²).

The spelling of 646645561 in words is "six hundred forty-six million, six hundred forty-five thousand, five hundred sixty-one".