81620994593 has 2 divisors, whose sum is σ = 81620994594. Its totient is φ = 81620994592.

The previous prime is 81620994577. The next prime is 81620994607. The reversal of 81620994593 is 39549902618.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 49868249344 + 31752745249 = 223312^2 + 178193^2 .

It is a cyclic number.

It is not a de Polignac number, because 81620994593 - 2⁴ = 81620994577 is a prime.

It is not a weakly prime, because it can be changed into another prime (81620994563) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40810497296 + 40810497297.

It is an arithmetic number, because the mean of its divisors is an integer number (40810497297).

Almost surely, 2^81620994593 is an apocalyptic number.

It is an amenable number.

81620994593 is a deficient number, since it is larger than the sum of its proper divisors (1).

81620994593 is an equidigital number, since it uses as much as digits as its factorization.

81620994593 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 4199040, while the sum is 56.

The spelling of 81620994593 in words is "eighty-one billion, six hundred twenty million, nine hundred ninety-four thousand, five hundred ninety-three".