81821998637 has 2 divisors, whose sum is σ = 81821998638. Its totient is φ = 81821998636.

The previous prime is 81821998613. The next prime is 81821998651. The reversal of 81821998637 is 73689912818.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 43810257481 + 38011741156 = 209309^2 + 194966^2 .

It is a cyclic number.

It is not a de Polignac number, because 81821998637 - 2⁸ = 81821998381 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 81821998637.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81821998607) 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, 40910999318 + 40910999319.

It is an arithmetic number, because the mean of its divisors is an integer number (40910999319).

Almost surely, 2^81821998637 is an apocalyptic number.

It is an amenable number.

81821998637 is a deficient number, since it is larger than the sum of its proper divisors (1).

81821998637 is an equidigital number, since it uses as much as digits as its factorization.

81821998637 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 10450944, while the sum is 62.

The spelling of 81821998637 in words is "eighty-one billion, eight hundred twenty-one million, nine hundred ninety-eight thousand, six hundred thirty-seven".