81919993 has 2 divisors, whose sum is σ = 81919994. Its totient is φ = 81919992.

The previous prime is 81919973. The next prime is 81920021. The reversal of 81919993 is 39991918.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 76685049 + 5234944 = 8757^2 + 2288^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-81919993 is a prime.

It is not a weakly prime, because it can be changed into another prime (81919973) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40959996 + 40959997.

It is an arithmetic number, because the mean of its divisors is an integer number (40959997).

Almost surely, 2^81919993 is an apocalyptic number.

It is an amenable number.

81919993 is a deficient number, since it is larger than the sum of its proper divisors (1).

81919993 is an equidigital number, since it uses as much as digits as its factorization.

81919993 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 157464, while the sum is 49.

The square root of 81919993 is about 9050.9664124888. The cubic root of 81919993 is about 434.3068062848.

The spelling of 81919993 in words is "eighty-one million, nine hundred nineteen thousand, nine hundred ninety-three".