81919989 has 12 divisors (see below), whose sum is σ = 119501772. Its totient is φ = 54072000.

The previous prime is 81919973. The next prime is 81919993. The reversal of 81919989 is 98991918.

It can be written as a sum of positive squares in 2 ways, for example, as 80407089 + 1512900 = 8967^2 + 1230^2 .

It is not a de Polignac number, because 81919989 - 2⁴ = 81919973 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81919909) 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 in 11 ways as a sum of consecutive naturals, for example, 44152 + ... + 45969.

It is an arithmetic number, because the mean of its divisors is an integer number (9958481).

Almost surely, 2^81919989 is an apocalyptic number.

It is an amenable number.

81919989 is a deficient number, since it is larger than the sum of its proper divisors (37581783).

81919989 is a wasteful number, since it uses less digits than its factorization.

81919989 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 90228 (or 90225 counting only the distinct ones).

The product of its digits is 419904, while the sum is 54.

The square root of 81919989 is about 9050.9661915179. The cubic root of 81919989 is about 434.3067992160.

The spelling of 81919989 in words is "eighty-one million, nine hundred nineteen thousand, nine hundred eighty-nine".