206642561 has 2 divisors, whose sum is σ = 206642562. Its totient is φ = 206642560.

The previous prime is 206642509. The next prime is 206642567. The reversal of 206642561 is 165246602.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 206640625 + 1936 = 14375^2 + 44^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-206642561 is a prime.

It is a super-2 number, since 2×206642561² = 85402296033277442, which contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (206642567) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 103321280 + 103321281.

It is an arithmetic number, because the mean of its divisors is an integer number (103321281).

Almost surely, 2^206642561 is an apocalyptic number.

It is an amenable number.

206642561 is a deficient number, since it is larger than the sum of its proper divisors (1).

206642561 is an equidigital number, since it uses as much as digits as its factorization.

206642561 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 17280, while the sum is 32.

The square root of 206642561 is about 14375.0673389727. The cubic root of 206642561 is about 591.2074868678.

The spelling of 206642561 in words is "two hundred six million, six hundred forty-two thousand, five hundred sixty-one".