3947789391661 has 2 divisors, whose sum is σ = 3947789391662. Its totient is φ = 3947789391660.

The previous prime is 3947789391659. The next prime is 3947789391697. The reversal of 3947789391661 is 1661939877493.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 3753247528900 + 194541862761 = 1937330^2 + 441069^2 .

It is a cyclic number.

It is not a de Polignac number, because 3947789391661 - 2¹ = 3947789391659 is a prime.

It is a super-2 number, since 2×3947789391661² (a number of 26 digits) contains 22 as substring.

Together with 3947789391659, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (3947789391631) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (23) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 1973894695830 + 1973894695831.

It is an arithmetic number, because the mean of its divisors is an integer number (1973894695831).

Almost surely, 2^{3947789391661} is an apocalyptic number.

It is an amenable number.

3947789391661 is a deficient number, since it is larger than the sum of its proper divisors (1).

3947789391661 is an equidigital number, since it uses as much as digits as its factorization.

3947789391661 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 370355328, while the sum is 73.

The spelling of 3947789391661 in words is "three trillion, nine hundred forty-seven billion, seven hundred eighty-nine million, three hundred ninety-one thousand, six hundred sixty-one".