391993681 has 2 divisors, whose sum is σ = 391993682. Its totient is φ = 391993680.

The previous prime is 391993649. The next prime is 391993697. The reversal of 391993681 is 186399193.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 330512400 + 61481281 = 18180^2 + 7841^2 .

It is an emirp because it is prime and its reverse (186399193) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 391993681 - 2⁵ = 391993649 is a prime.

It is a super-4 number, since 4×391993681⁴ (a number of 35 digits) contains 4444 as substring. Note that it is a super-d number also for d = 2.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (391990681) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 195996840 + 195996841.

It is an arithmetic number, because the mean of its divisors is an integer number (195996841).

Almost surely, 2^391993681 is an apocalyptic number.

It is an amenable number.

391993681 is a deficient number, since it is larger than the sum of its proper divisors (1).

391993681 is an equidigital number, since it uses as much as digits as its factorization.

391993681 is an evil number, because the sum of its binary digits is even.

The product of its digits is 314928, while the sum is 49.

The square root of 391993681 is about 19798.8302937320. The cubic root of 391993681 is about 731.8572094745.

The spelling of 391993681 in words is "three hundred ninety-one million, nine hundred ninety-three thousand, six hundred eighty-one".