391921897 has 2 divisors, whose sum is σ = 391921898. Its totient is φ = 391921896.

The previous prime is 391921883. The next prime is 391921919. The reversal of 391921897 is 798129193.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 285914281 + 106007616 = 16909^2 + 10296^2 .

It is a cyclic number.

It is not a de Polignac number, because 391921897 - 2¹¹ = 391919849 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 391921897.

It is not a weakly prime, because it can be changed into another prime (391921997) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 195960948 + 195960949.

It is an arithmetic number, because the mean of its divisors is an integer number (195960949).

Almost surely, 2^391921897 is an apocalyptic number.

It is an amenable number.

391921897 is a deficient number, since it is larger than the sum of its proper divisors (1).

391921897 is an equidigital number, since it uses as much as digits as its factorization.

391921897 is an evil number, because the sum of its binary digits is even.

The product of its digits is 244944, while the sum is 49.

The square root of 391921897 is about 19797.0173763625. The cubic root of 391921897 is about 731.8125328656.

The spelling of 391921897 in words is "three hundred ninety-one million, nine hundred twenty-one thousand, eight hundred ninety-seven".