77987561 has 2 divisors, whose sum is σ = 77987562. Its totient is φ = 77987560.

The previous prime is 77987521. The next prime is 77987573. The reversal of 77987561 is 16578977.

77987561 = 6244² + 6245².

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 39000025 + 38987536 = 6245^2 + 6244^2 .

It is an emirp because it is prime and its reverse (16578977) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 77987561 - 2¹⁴ = 77971177 is a prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (77987501) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 38993780 + 38993781.

It is an arithmetic number, because the mean of its divisors is an integer number (38993781).

Almost surely, 2^77987561 is an apocalyptic number.

77987561 is the 6245-th centered square number.

It is an amenable number.

77987561 is a deficient number, since it is larger than the sum of its proper divisors (1).

77987561 is an equidigital number, since it uses as much as digits as its factorization.

77987561 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 740880, while the sum is 50.

The square root of 77987561 is about 8831.0566185480. The cubic root of 77987561 is about 427.2431543122.

The spelling of 77987561 in words is "seventy-seven million, nine hundred eighty-seven thousand, five hundred sixty-one".