16561661 has 2 divisors, whose sum is σ = 16561662. Its totient is φ = 16561660.

The previous prime is 16561627. The next prime is 16561667. The reversal of 16561661 is 16616561.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 16556761 + 4900 = 4069^2 + 70^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-16561661 is a prime.

It is a Sophie Germain prime.

It is a Curzon number.

It is equal to p_1064858 and since 16561661 and 1064858 have the same sum of digits, it is a Honaker prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (16561667) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 8280830 + 8280831.

It is an arithmetic number, because the mean of its divisors is an integer number (8280831).

Almost surely, 2^16561661 is an apocalyptic number.

It is an amenable number.

16561661 is a deficient number, since it is larger than the sum of its proper divisors (1).

16561661 is an equidigital number, since it uses as much as digits as its factorization.

16561661 is an evil number, because the sum of its binary digits is even.

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

The square root of 16561661 is about 4069.6020689989. The cubic root of 16561661 is about 254.8989013560.

The spelling of 16561661 in words is "sixteen million, five hundred sixty-one thousand, six hundred sixty-one".