77581981 has 2 divisors, whose sum is σ = 77581982. Its totient is φ = 77581980.

The previous prime is 77581979. The next prime is 77581993. The reversal of 77581981 is 18918577.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 70644025 + 6937956 = 8405^2 + 2634^2 .

It is an emirp because it is prime and its reverse (18918577) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 77581981 - 2¹ = 77581979 is a prime.

It is a super-2 number, since 2×77581981² = 12037927551768722, which contains 22 as substring.

Together with 77581979, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (77581951) 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, 38790990 + 38790991.

It is an arithmetic number, because the mean of its divisors is an integer number (38790991).

Almost surely, 2^77581981 is an apocalyptic number.

It is an amenable number.

77581981 is a deficient number, since it is larger than the sum of its proper divisors (1).

77581981 is an equidigital number, since it uses as much as digits as its factorization.

77581981 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 141120, while the sum is 46.

The square root of 77581981 is about 8808.0634080370. The cubic root of 77581981 is about 426.5012302818.

The spelling of 77581981 in words is "seventy-seven million, five hundred eighty-one thousand, nine hundred eighty-one".