78721549 has 2 divisors, whose sum is σ = 78721550. Its totient is φ = 78721548.

The previous prime is 78721529. The next prime is 78721597. The reversal of 78721549 is 94512787.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 66422500 + 12299049 = 8150^2 + 3507^2 .

It is a cyclic number.

It is not a de Polignac number, because 78721549 - 2⁷ = 78721421 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (78721529) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 39360774 + 39360775.

It is an arithmetic number, because the mean of its divisors is an integer number (39360775).

Almost surely, 2^78721549 is an apocalyptic number.

It is an amenable number.

78721549 is a deficient number, since it is larger than the sum of its proper divisors (1).

78721549 is an equidigital number, since it uses as much as digits as its factorization.

78721549 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 141120, while the sum is 43.

The square root of 78721549 is about 8872.5164975896. The cubic root of 78721549 is about 428.5793189394.

The spelling of 78721549 in words is "seventy-eight million, seven hundred twenty-one thousand, five hundred forty-nine".