78722821 has 2 divisors, whose sum is σ = 78722822. Its totient is φ = 78722820.

The previous prime is 78722773. The next prime is 78722827. The reversal of 78722821 is 12822787.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 49140100 + 29582721 = 7010^2 + 5439^2 .

It is an emirp because it is prime and its reverse (12822787) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 78722821 - 2⁹ = 78722309 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (78722827) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 39361410 + 39361411.

It is an arithmetic number, because the mean of its divisors is an integer number (39361411).

Almost surely, 2^78722821 is an apocalyptic number.

It is an amenable number.

78722821 is a deficient number, since it is larger than the sum of its proper divisors (1).

78722821 is an equidigital number, since it uses as much as digits as its factorization.

78722821 is an evil number, because the sum of its binary digits is even.

The product of its digits is 25088, while the sum is 37.

The square root of 78722821 is about 8872.5881793308. The cubic root of 78722821 is about 428.5816272864.

The spelling of 78722821 in words is "seventy-eight million, seven hundred twenty-two thousand, eight hundred twenty-one".