681617861 has 2 divisors, whose sum is σ = 681617862. Its totient is φ = 681617860.

The previous prime is 681617831. The next prime is 681617869. The reversal of 681617861 is 168716186.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 382984900 + 298632961 = 19570^2 + 17281^2 .

It is a cyclic number.

It is not a de Polignac number, because 681617861 - 2¹⁴ = 681601477 is a prime.

It is a Sophie Germain prime.

It is a Curzon number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (681617869) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 340808930 + 340808931.

It is an arithmetic number, because the mean of its divisors is an integer number (340808931).

Almost surely, 2^681617861 is an apocalyptic number.

It is an amenable number.

681617861 is a deficient number, since it is larger than the sum of its proper divisors (1).

681617861 is an equidigital number, since it uses as much as digits as its factorization.

681617861 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 681617861 is about 26107.8122599348. The cubic root of 681617861 is about 880.0627800425.

The spelling of 681617861 in words is "six hundred eighty-one million, six hundred seventeen thousand, eight hundred sixty-one".