778126721 has 2 divisors, whose sum is σ = 778126722. Its totient is φ = 778126720.

The previous prime is 778126711. The next prime is 778126729. The reversal of 778126721 is 127621877.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 582546496 + 195580225 = 24136^2 + 13985^2 .

It is a cyclic number.

It is not a de Polignac number, because 778126721 - 2¹⁴ = 778110337 is a prime.

It is not a weakly prime, because it can be changed into another prime (778126729) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 389063360 + 389063361.

It is an arithmetic number, because the mean of its divisors is an integer number (389063361).

Almost surely, 2^778126721 is an apocalyptic number.

It is an amenable number.

778126721 is a deficient number, since it is larger than the sum of its proper divisors (1).

778126721 is an equidigital number, since it uses as much as digits as its factorization.

778126721 is an evil number, because the sum of its binary digits is even.

The product of its digits is 65856, while the sum is 41.

The square root of 778126721 is about 27894.9228534513. The cubic root of 778126721 is about 919.7789012639.

The spelling of 778126721 in words is "seven hundred seventy-eight million, one hundred twenty-six thousand, seven hundred twenty-one".