77997781 has 2 divisors, whose sum is σ = 77997782. Its totient is φ = 77997780.

The previous prime is 77997779. The next prime is 77997809. The reversal of 77997781 is 18779977.

It is the 3606-th star number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 76475025 + 1522756 = 8745^2 + 1234^2 .

It is an emirp because it is prime and its reverse (18779977) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 77997781 - 2¹ = 77997779 is a prime.

It is a super-2 number, since 2×77997781² = 12167307681847922, which contains 22 as substring.

Together with 77997779, it forms a pair of twin primes.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (77997721) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 38998890 + 38998891.

It is an arithmetic number, because the mean of its divisors is an integer number (38998891).

Almost surely, 2^77997781 is an apocalyptic number.

It is an amenable number.

77997781 is a deficient number, since it is larger than the sum of its proper divisors (1).

77997781 is an equidigital number, since it uses as much as digits as its factorization.

77997781 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 1555848, while the sum is 55.

The square root of 77997781 is about 8831.6352392974. The cubic root of 77997781 is about 427.2618164093.

The spelling of 77997781 in words is "seventy-seven million, nine hundred ninety-seven thousand, seven hundred eighty-one".