81990689 has 12 divisors (see below), whose sum is σ = 91027860. Its totient is φ = 73788000.

The previous prime is 81990683. The next prime is 81990709. The reversal of 81990689 is 98609918.

It can be written as a sum of positive squares in 2 ways, for example, as 68973025 + 13017664 = 8305^2 + 3608^2 .

It is not a de Polignac number, because 81990689 - 2¹⁶ = 81925153 is a prime.

It is not an unprimeable number, because it can be changed into a prime (81990683) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 8867 + ... + 15575.

It is an arithmetic number, because the mean of its divisors is an integer number (7585655).

Almost surely, 2^81990689 is an apocalyptic number.

It is an amenable number.

81990689 is a deficient number, since it is larger than the sum of its proper divisors (9037171).

81990689 is a wasteful number, since it uses less digits than its factorization.

81990689 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6832 (or 6821 counting only the distinct ones).

The product of its (nonzero) digits is 279936, while the sum is 50.

The square root of 81990689 is about 9054.8710095727. The cubic root of 81990689 is about 434.4317042686.

The spelling of 81990689 in words is "eighty-one million, nine hundred ninety thousand, six hundred eighty-nine".