78664847581 has 2 divisors, whose sum is σ = 78664847582. Its totient is φ = 78664847580.

The previous prime is 78664847563. The next prime is 78664847587. The reversal of 78664847581 is 18574846687.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 72657202500 + 6007645081 = 269550^2 + 77509^2 .

It is an emirp because it is prime and its reverse (18574846687) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 78664847581 - 2²³ = 78656458973 is a prime.

It is a super-2 number, since 2×78664847581² (a number of 23 digits) contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (78664847587) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 39332423790 + 39332423791.

It is an arithmetic number, because the mean of its divisors is an integer number (39332423791).

Almost surely, 2^78664847581 is an apocalyptic number.

It is an amenable number.

78664847581 is a deficient number, since it is larger than the sum of its proper divisors (1).

78664847581 is an equidigital number, since it uses as much as digits as its factorization.

78664847581 is an evil number, because the sum of its binary digits is even.

The product of its digits is 72253440, while the sum is 64.

The spelling of 78664847581 in words is "seventy-eight billion, six hundred sixty-four million, eight hundred forty-seven thousand, five hundred eighty-one".