199609661 has 2 divisors, whose sum is σ = 199609662. Its totient is φ = 199609660.

The previous prime is 199609603. The next prime is 199609673. The reversal of 199609661 is 166906991.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 148986436 + 50623225 = 12206^2 + 7115^2 .

It is an emirp because it is prime and its reverse (166906991) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 199609661 - 2¹⁸ = 199347517 is a prime.

It is a Sophie Germain prime.

199609661 is a strobogrammatic number because it is the same when read upside-down.

It is a Curzon number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (199609601) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 99804830 + 99804831.

It is an arithmetic number, because the mean of its divisors is an integer number (99804831).

Almost surely, 2^199609661 is an apocalyptic number.

It is an amenable number.

199609661 is a deficient number, since it is larger than the sum of its proper divisors (1).

199609661 is an equidigital number, since it uses as much as digits as its factorization.

199609661 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 157464, while the sum is 47.

The square root of 199609661 is about 14128.3283158341. The cubic root of 199609661 is about 584.4228471447.

The spelling of 199609661 in words is "one hundred ninety-nine million, six hundred nine thousand, six hundred sixty-one".