81530913125809 has 9 divisors (see below), whose sum is σ = 94842156141291. Its totient is φ = 69883585645440.

The previous prime is 81530913125759. The next prime is 81530913125821. The reversal of 81530913125809 is 90852131903518.

It is a happy number.

The square root of 81530913125809 is 9029447.

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

It can be written as a sum of positive squares in only one way, i.e., 2090057164209 + 79440855961600 = 1445703^2 + 8912960^2 .

It is not a de Polignac number, because 81530913125809 - 2²⁹ = 81530376254897 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 81530913125809.

It is not an unprimeable number, because it can be changed into a prime (81530913125839) by changing a digit.

It is a polite number, since it can be written in 8 ways as a sum of consecutive naturals, for example, 62561169 + ... + 63851089.

Almost surely, 2^{81530913125809} is an apocalyptic number.

81530913125809 is the 9029447-th square number.

81530913125809 is the 4514724-th centered octagonal number.

It is an amenable number.

81530913125809 is a deficient number, since it is larger than the sum of its proper divisors (13311243015482).

81530913125809 is an frugal number, since it uses more digits than its factorization.

81530913125809 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2579856 (or 1289928 counting only the distinct ones).

The product of its (nonzero) digits is 2332800, while the sum is 55.

The spelling of 81530913125809 in words is "eighty-one trillion, five hundred thirty billion, nine hundred thirteen million, one hundred twenty-five thousand, eight hundred nine".