391961981 has 2 divisors, whose sum is σ = 391961982. Its totient is φ = 391961980.

The previous prime is 391961953. The next prime is 391962019. The reversal of 391961981 is 189169193.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 344696356 + 47265625 = 18566^2 + 6875^2 .

It is a cyclic number.

It is not a de Polignac number, because 391961981 - 2⁶ = 391961917 is a prime.

It is a super-2 number, since 2×391961981² = 307268389098888722, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (391961281) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 195980990 + 195980991.

It is an arithmetic number, because the mean of its divisors is an integer number (195980991).

Almost surely, 2^391961981 is an apocalyptic number.

It is an amenable number.

391961981 is a deficient number, since it is larger than the sum of its proper divisors (1).

391961981 is an equidigital number, since it uses as much as digits as its factorization.

391961981 is an evil number, because the sum of its binary digits is even.

The product of its digits is 104976, while the sum is 47.

The square root of 391961981 is about 19798.0297252025. The cubic root of 391961981 is about 731.8374808410.

The spelling of 391961981 in words is "three hundred ninety-one million, nine hundred sixty-one thousand, nine hundred eighty-one".