780721 has 2 divisors, whose sum is σ = 780722. Its totient is φ = 780720.

The previous prime is 780719. The next prime is 780733. The reversal of 780721 is 127087.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 746496 + 34225 = 864^2 + 185^2 .

It is a cyclic number.

It is not a de Polignac number, because 780721 - 2¹ = 780719 is a prime.

Together with 780719, it forms a pair of twin primes.

It is not a weakly prime, because it can be changed into another prime (780421) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 390360 + 390361.

It is an arithmetic number, because the mean of its divisors is an integer number (390361).

2⁷⁸⁰⁷²¹ is an apocalyptic number.

It is an amenable number.

780721 is a deficient number, since it is larger than the sum of its proper divisors (1).

780721 is an equidigital number, since it uses as much as digits as its factorization.

780721 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 784, while the sum is 25.

The square root of 780721 is about 883.5841782196. The cubic root of 780721 is about 92.0799950106.

The spelling of 780721 in words is "seven hundred eighty thousand, seven hundred twenty-one".