77731991 has 2 divisors, whose sum is σ = 77731992. Its totient is φ = 77731990.

The previous prime is 77731981. The next prime is 77731999. The reversal of 77731991 is 19913777.

It is a happy number.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 77731991 - 2¹⁴ = 77715607 is a prime.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (77731999) 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, 38865995 + 38865996.

It is an arithmetic number, because the mean of its divisors is an integer number (38865996).

Almost surely, 2^77731991 is an apocalyptic number.

77731991 is a deficient number, since it is larger than the sum of its proper divisors (1).

77731991 is an equidigital number, since it uses as much as digits as its factorization.

77731991 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 83349, while the sum is 44.

The square root of 77731991 is about 8816.5747884312. The cubic root of 77731991 is about 426.7759429439.

It can be divided in two parts, 777 and 31991, that added together give a 15-th power (32768 = 2¹⁵).

The spelling of 77731991 in words is "seventy-seven million, seven hundred thirty-one thousand, nine hundred ninety-one".