291721 has 2 divisors, whose sum is σ = 291722. Its totient is φ = 291720.

The previous prime is 291701. The next prime is 291727. The reversal of 291721 is 127192.

It is the 221-st star number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 291600 + 121 = 540^2 + 11^2 .

It is a cyclic number.

It is not a de Polignac number, because 291721 - 2⁵ = 291689 is a prime.

It is a super-2 number, since 2×291721² = 170202283682, which contains 22 as substring.

It is a Chen prime.

It is a junction number, because it is equal to n+sod(n) for n = 291692 and 291701.

It is not a weakly prime, because it can be changed into another prime (291727) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 145860 + 145861.

It is an arithmetic number, because the mean of its divisors is an integer number (145861).

2²⁹¹⁷²¹ is an apocalyptic number.

It is an amenable number.

291721 is a deficient number, since it is larger than the sum of its proper divisors (1).

291721 is an equidigital number, since it uses as much as digits as its factorization.

291721 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 252, while the sum is 22.

The square root of 291721 is about 540.1120254169. The cubic root of 291721 is about 66.3217378843.

The spelling of 291721 in words is "two hundred ninety-one thousand, seven hundred twenty-one".