78518521 has 2 divisors, whose sum is σ = 78518522. Its totient is φ = 78518520.

The previous prime is 78518519. The next prime is 78518533. The reversal of 78518521 is 12581587.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 63425296 + 15093225 = 7964^2 + 3885^2 .

It is an emirp because it is prime and its reverse (12581587) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 78518521 - 2¹ = 78518519 is a prime.

Together with 78518519, it forms a pair of twin primes.

It is not a weakly prime, because it can be changed into another prime (78518501) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 39259260 + 39259261.

It is an arithmetic number, because the mean of its divisors is an integer number (39259261).

Almost surely, 2^78518521 is an apocalyptic number.

It is an amenable number.

78518521 is a deficient number, since it is larger than the sum of its proper divisors (1).

78518521 is an equidigital number, since it uses as much as digits as its factorization.

78518521 is an evil number, because the sum of its binary digits is even.

The product of its digits is 22400, while the sum is 37.

The square root of 78518521 is about 8861.0677121891. The cubic root of 78518521 is about 428.2105570818.

It can be divided in two parts, 785 and 18521, that added together give a triangular number (19306 = T₁₉₆).

The spelling of 78518521 in words is "seventy-eight million, five hundred eighteen thousand, five hundred twenty-one".