78721 has 2 divisors, whose sum is σ = 78722. Its totient is φ = 78720.

The previous prime is 78713. The next prime is 78737. The reversal of 78721 is 12787.

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., 69696 + 9025 = 264^2 + 95^2 .

It is a cyclic number.

It is not a de Polignac number, because 78721 - 2³ = 78713 is a prime.

It is an alternating number because its digits alternate between odd and even.

It is not a weakly prime, because it can be changed into another prime (78781) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 39360 + 39361.

It is an arithmetic number, because the mean of its divisors is an integer number (39361).

2⁷⁸⁷²¹ is an apocalyptic number.

It is an amenable number.

78721 is a deficient number, since it is larger than the sum of its proper divisors (1).

78721 is an equidigital number, since it uses as much as digits as its factorization.

78721 is an odious number, because the sum of its binary digits is odd.

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

The square root of 78721 is about 280.5726287434. The cubic root of 78721 is about 42.8578322640.

It can be divided in two parts, 787 and 21, that added together give a palindrome (808).

The spelling of 78721 in words is "seventy-eight thousand, seven hundred twenty-one".