81691920503 has 2 divisors, whose sum is σ = 81691920504. Its totient is φ = 81691920502.

The previous prime is 81691920481. The next prime is 81691920521. The reversal of 81691920503 is 30502919618.

It is a happy number.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 81691920503 - 2³⁶ = 12972443767 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81691920103) 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, 40845960251 + 40845960252.

It is an arithmetic number, because the mean of its divisors is an integer number (40845960252).

Almost surely, 2^81691920503 is an apocalyptic number.

81691920503 is a deficient number, since it is larger than the sum of its proper divisors (1).

81691920503 is an equidigital number, since it uses as much as digits as its factorization.

81691920503 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 116640, while the sum is 44.

The spelling of 81691920503 in words is "eighty-one billion, six hundred ninety-one million, nine hundred twenty thousand, five hundred three".