8181781 has 2 divisors, whose sum is σ = 8181782. Its totient is φ = 8181780.

The previous prime is 8181751. The next prime is 8181791. The reversal of 8181781 is 1871818.

8181781 is digitally balanced in base 3, because in such base it contains all the possibile digits an equal number of times.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 5716881 + 2464900 = 2391^2 + 1570^2 .

It is a cyclic number.

It is not a de Polignac number, because 8181781 - 2⁹ = 8181269 is a prime.

It is a super-2 number, since 2×8181781² = 133883080663922, which contains 22 as substring.

8181781 is a lucky number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (8181731) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 4090890 + 4090891.

It is an arithmetic number, because the mean of its divisors is an integer number (4090891).

Almost surely, 2^8181781 is an apocalyptic number.

It is an amenable number.

8181781 is a deficient number, since it is larger than the sum of its proper divisors (1).

8181781 is an equidigital number, since it uses as much as digits as its factorization.

8181781 is an evil number, because the sum of its binary digits is even.

The product of its digits is 3584, while the sum is 34.

The square root of 8181781 is about 2860.3812682927. The cubic root of 8181781 is about 201.5035106228.

The spelling of 8181781 in words is "eight million, one hundred eighty-one thousand, seven hundred eighty-one".