839721661 has 2 divisors, whose sum is σ = 839721662. Its totient is φ = 839721660.

The previous prime is 839721643. The next prime is 839721677. The reversal of 839721661 is 166127938.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 420496036 + 419225625 = 20506^2 + 20475^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-839721661 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (839721601) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 419860830 + 419860831.

It is an arithmetic number, because the mean of its divisors is an integer number (419860831).

Almost surely, 2^839721661 is an apocalyptic number.

It is an amenable number.

839721661 is a deficient number, since it is larger than the sum of its proper divisors (1).

839721661 is an equidigital number, since it uses as much as digits as its factorization.

839721661 is an evil number, because the sum of its binary digits is even.

The product of its digits is 108864, while the sum is 43.

The square root of 839721661 is about 28977.9512905933. The cubic root of 839721661 is about 943.4345688182.

It can be divided in two parts, 839 and 721661, that added together give a square (722500 = 850²).

The spelling of 839721661 in words is "eight hundred thirty-nine million, seven hundred twenty-one thousand, six hundred sixty-one".