817681661 has 2 divisors, whose sum is σ = 817681662. Its totient is φ = 817681660.

The previous prime is 817681643. The next prime is 817681723. The reversal of 817681661 is 166186718.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 805992100 + 11689561 = 28390^2 + 3419^2 .

It is a cyclic number.

It is not a de Polignac number, because 817681661 - 2⁶ = 817681597 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (817681621) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 408840830 + 408840831.

It is an arithmetic number, because the mean of its divisors is an integer number (408840831).

Almost surely, 2^817681661 is an apocalyptic number.

It is an amenable number.

817681661 is a deficient number, since it is larger than the sum of its proper divisors (1).

817681661 is an equidigital number, since it uses as much as digits as its factorization.

817681661 is an evil number, because the sum of its binary digits is even.

The product of its digits is 96768, while the sum is 44.

The square root of 817681661 is about 28595.1335195344. The cubic root of 817681661 is about 935.1072392655.

The spelling of 817681661 in words is "eight hundred seventeen million, six hundred eighty-one thousand, six hundred sixty-one".