78828721 has 2 divisors, whose sum is σ = 78828722. Its totient is φ = 78828720.

The previous prime is 78828713. The next prime is 78828731. The reversal of 78828721 is 12782887.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 76755121 + 2073600 = 8761^2 + 1440^2 .

It is a cyclic number.

It is not a de Polignac number, because 78828721 - 2³ = 78828713 is a prime.

It is not a weakly prime, because it can be changed into another prime (78828731) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 39414360 + 39414361.

It is an arithmetic number, because the mean of its divisors is an integer number (39414361).

Almost surely, 2^78828721 is an apocalyptic number.

It is an amenable number.

78828721 is a deficient number, since it is larger than the sum of its proper divisors (1).

78828721 is an equidigital number, since it uses as much as digits as its factorization.

78828721 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 100352, while the sum is 43.

The square root of 78828721 is about 8878.5539926274. The cubic root of 78828721 is about 428.7737209178.

The spelling of 78828721 in words is "seventy-eight million, eight hundred twenty-eight thousand, seven hundred twenty-one".