81809121 has 8 divisors (see below), whose sum is σ = 110203744. Its totient is φ = 53976960.

The previous prime is 81809069. The next prime is 81809149. The reversal of 81809121 is 12190818.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 81809121 - 2⁹ = 81808609 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (81809921) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 140275 + ... + 140856.

It is an arithmetic number, because the mean of its divisors is an integer number (13775468).

Almost surely, 2^81809121 is an apocalyptic number.

It is an amenable number.

81809121 is a deficient number, since it is larger than the sum of its proper divisors (28394623).

81809121 is a wasteful number, since it uses less digits than its factorization.

81809121 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 281231.

The product of its (nonzero) digits is 1152, while the sum is 30.

The square root of 81809121 is about 9044.8394678955. The cubic root of 81809121 is about 434.1107849300.

Adding to 81809121 its reverse (12190818), we get a palindrome (93999939).

The spelling of 81809121 in words is "eighty-one million, eight hundred nine thousand, one hundred twenty-one".