81994604409 has 27 divisors (see below), whose sum is σ = 122420190789. Its totient is φ = 52882563960.

The previous prime is 81994604387. The next prime is 81994604473. The reversal of 81994604409 is 90440649918.

It is a happy number.

The square root of 81994604409 is 286347.

It is a perfect power (a square), and thus also a powerful number.

81994604409 is a `hidden beast` number, since 8 + 199 + 4 + 6 + 0 + 440 + 9 = 666.

It is not a de Polignac number, because 81994604409 - 2⁷ = 81994604281 is a prime.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (81994600409) by changing a digit.

It is a polite number, since it can be written in 26 ways as a sum of consecutive naturals, for example, 26628732 + ... + 26631810.

Almost surely, 2^81994604409 is an apocalyptic number.

81994604409 is the 286347-th square number.

81994604409 is the 143174-th centered octagonal number.

It is an amenable number.

81994604409 is a deficient number, since it is larger than the sum of its proper divisors (40425586380).

81994604409 is an frugal number, since it uses more digits than its factorization.

81994604409 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6226 (or 3113 counting only the distinct ones).

The product of its (nonzero) digits is 2239488, while the sum is 54.

The spelling of 81994604409 in words is "eighty-one billion, nine hundred ninety-four million, six hundred four thousand, four hundred nine".