81948781 has 2 divisors, whose sum is σ = 81948782. Its totient is φ = 81948780.

The previous prime is 81948749. The next prime is 81948859. The reversal of 81948781 is 18784918.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 49070025 + 32878756 = 7005^2 + 5734^2 .

It is a cyclic number.

It is not a de Polignac number, because 81948781 - 2⁵ = 81948749 is a prime.

It is a super-2 number, since 2×81948781² = 13431205414771922, which contains 22 as substring.

It is equal to p_4776589 and since 81948781 and 4776589 have the same sum of digits, it is a Honaker prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81948731) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40974390 + 40974391.

It is an arithmetic number, because the mean of its divisors is an integer number (40974391).

Almost surely, 2^81948781 is an apocalyptic number.

It is an amenable number.

81948781 is a deficient number, since it is larger than the sum of its proper divisors (1).

81948781 is an equidigital number, since it uses as much as digits as its factorization.

81948781 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 129024, while the sum is 46.

The square root of 81948781 is about 9052.5566002097. The cubic root of 81948781 is about 434.3576744534.

The spelling of 81948781 in words is "eighty-one million, nine hundred forty-eight thousand, seven hundred eighty-one".