99777781 has 2 divisors, whose sum is σ = 99777782. Its totient is φ = 99777780.

The previous prime is 99777779. The next prime is 99777803. The reversal of 99777781 is 18777799.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 67798756 + 31979025 = 8234^2 + 5655^2 .

It is a cyclic number.

It is not a de Polignac number, because 99777781 - 2¹ = 99777779 is a prime.

It is a super-2 number, since 2×99777781² = 19911211162567922, which contains 22 as substring.

Together with 99777779, 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 (99777731) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 49888890 + 49888891.

It is an arithmetic number, because the mean of its divisors is an integer number (49888891).

Almost surely, 2^99777781 is an apocalyptic number.

It is an amenable number.

99777781 is a deficient number, since it is larger than the sum of its proper divisors (1).

99777781 is an equidigital number, since it uses as much as digits as its factorization.

99777781 is an evil number, because the sum of its binary digits is even.

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

The square root of 99777781 is about 9988.8828704716. The cubic root of 99777781 is about 463.8148119616.

The spelling of 99777781 in words is "ninety-nine million, seven hundred seventy-seven thousand, seven hundred eighty-one".