391921 has 2 divisors, whose sum is σ = 391922. Its totient is φ = 391920.

The previous prime is 391907. The next prime is 391939. The reversal of 391921 is 129193.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 390625 + 1296 = 625^2 + 36^2 .

It is an emirp because it is prime and its reverse (129193) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 391921 - 2⁵ = 391889 is a prime.

It is not a weakly prime, because it can be changed into another prime (391961) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 195960 + 195961.

It is an arithmetic number, because the mean of its divisors is an integer number (195961).

2³⁹¹⁹²¹ is an apocalyptic number.

It is an amenable number.

391921 is a deficient number, since it is larger than the sum of its proper divisors (1).

391921 is an equidigital number, since it uses as much as digits as its factorization.

391921 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 486, while the sum is 25.

The square root of 391921 is about 626.0359414602. The cubic root of 391921 is about 73.1811974560.

It can be divided in two parts, 39192 and 1, that added together give a palindrome (39193).

The spelling of 391921 in words is "three hundred ninety-one thousand, nine hundred twenty-one".