391051721 has 2 divisors, whose sum is σ = 391051722. Its totient is φ = 391051720.

The previous prime is 391051693. The next prime is 391051733. The reversal of 391051721 is 127150193.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 385926025 + 5125696 = 19645^2 + 2264^2 .

It is a cyclic number.

It is not a de Polignac number, because 391051721 - 2⁶ = 391051657 is a prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (391051751) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 195525860 + 195525861.

It is an arithmetic number, because the mean of its divisors is an integer number (195525861).

Almost surely, 2^391051721 is an apocalyptic number.

It is an amenable number.

391051721 is a deficient number, since it is larger than the sum of its proper divisors (1).

391051721 is an equidigital number, since it uses as much as digits as its factorization.

391051721 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 1890, while the sum is 29.

The square root of 391051721 is about 19775.0277117379. The cubic root of 391051721 is about 731.2705221698.

The spelling of 391051721 in words is "three hundred ninety-one million, fifty-one thousand, seven hundred twenty-one".