78815557 has 2 divisors, whose sum is σ = 78815558. Its totient is φ = 78815556.

The previous prime is 78815543. The next prime is 78815713. The reversal of 78815557 is 75551887.

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., 44076321 + 34739236 = 6639^2 + 5894^2 .

It is a cyclic number.

It is not a de Polignac number, because 78815557 - 2¹¹ = 78813509 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (78815257) 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, 39407778 + 39407779.

It is an arithmetic number, because the mean of its divisors is an integer number (39407779).

Almost surely, 2^78815557 is an apocalyptic number.

It is an amenable number.

78815557 is a deficient number, since it is larger than the sum of its proper divisors (1).

78815557 is an equidigital number, since it uses as much as digits as its factorization.

78815557 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 392000, while the sum is 46.

The square root of 78815557 is about 8877.8126247404. The cubic root of 78815557 is about 428.7498519041.

The spelling of 78815557 in words is "seventy-eight million, eight hundred fifteen thousand, five hundred fifty-seven".