840291721 has 2 divisors, whose sum is σ = 840291722. Its totient is φ = 840291720.

The previous prime is 840291707. The next prime is 840291743. The reversal of 840291721 is 127192048.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 827367696 + 12924025 = 28764^2 + 3595^2 .

It is a cyclic number.

It is not a de Polignac number, because 840291721 - 2⁹ = 840291209 is a prime.

It is a super-2 number, since 2×840291721² = 1412180352762283682, which contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (840297721) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 420145860 + 420145861.

It is an arithmetic number, because the mean of its divisors is an integer number (420145861).

Almost surely, 2^840291721 is an apocalyptic number.

It is an amenable number.

840291721 is a deficient number, since it is larger than the sum of its proper divisors (1).

840291721 is an equidigital number, since it uses as much as digits as its factorization.

840291721 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 8064, while the sum is 34.

The square root of 840291721 is about 28987.7857208860. The cubic root of 840291721 is about 943.6480096441.

The spelling of 840291721 in words is "eight hundred forty million, two hundred ninety-one thousand, seven hundred twenty-one".