77868191981 has 2 divisors, whose sum is σ = 77868191982. Its totient is φ = 77868191980.

The previous prime is 77868191969. The next prime is 77868192013. The reversal of 77868191981 is 18919186877.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 70397355625 + 7470836356 = 265325^2 + 86434^2 .

It is a cyclic number.

It is not a de Polignac number, because 77868191981 - 2²² = 77863997677 is a prime.

It is a super-2 number, since 2×77868191981² (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 (77868161981) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 38934095990 + 38934095991.

It is an arithmetic number, because the mean of its divisors is an integer number (38934095991).

Almost surely, 2^77868191981 is an apocalyptic number.

It is an amenable number.

77868191981 is a deficient number, since it is larger than the sum of its proper divisors (1).

77868191981 is an equidigital number, since it uses as much as digits as its factorization.

77868191981 is an evil number, because the sum of its binary digits is even.

The product of its digits is 12192768, while the sum is 65.

The spelling of 77868191981 in words is "seventy-seven billion, eight hundred sixty-eight million, one hundred ninety-one thousand, nine hundred eighty-one".