77987981 has 2 divisors, whose sum is σ = 77987982. Its totient is φ = 77987980.

The previous prime is 77987957. The next prime is 77988049. The reversal of 77987981 is 18978977.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 39175081 + 38812900 = 6259^2 + 6230^2 .

It is a cyclic number.

It is not a de Polignac number, because 77987981 - 2¹⁰ = 77986957 is a prime.

It is a super-2 number, since 2×77987981² = 12164250360912722, which contains 22 as substring.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (77987281) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 38993990 + 38993991.

It is an arithmetic number, because the mean of its divisors is an integer number (38993991).

Almost surely, 2^77987981 is an apocalyptic number.

It is an amenable number.

77987981 is a deficient number, since it is larger than the sum of its proper divisors (1).

77987981 is an equidigital number, since it uses as much as digits as its factorization.

77987981 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 1778112, while the sum is 56.

The square root of 77987981 is about 8831.0803982299. The cubic root of 77987981 is about 427.2439212798.

The spelling of 77987981 in words is "seventy-seven million, nine hundred eighty-seven thousand, nine hundred eighty-one".