81506121481 has 4 divisors (see below), whose sum is σ = 81511171092. Its totient is φ = 81501071872.

The previous prime is 81506121467. The next prime is 81506121491. The reversal of 81506121481 is 18412160518.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 18412160518 = 2 ⋅9206080259.

It can be written as a sum of positive squares in 2 ways, for example, as 51096342025 + 30409779456 = 226045^2 + 174384^2 .

It is a cyclic number.

It is not a de Polignac number, because 81506121481 - 2⁷ = 81506121353 is a prime.

It is a super-2 number, since 2×81506121481² (a number of 23 digits) contains 22 as substring.

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 81506121481.

It is not an unprimeable number, because it can be changed into a prime (81506121451) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2500516 + ... + 2532901.

It is an arithmetic number, because the mean of its divisors is an integer number (20377792773).

Almost surely, 2^81506121481 is an apocalyptic number.

It is an amenable number.

81506121481 is a deficient number, since it is larger than the sum of its proper divisors (5049611).

81506121481 is a wasteful number, since it uses less digits than its factorization.

81506121481 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5049610.

The product of its (nonzero) digits is 15360, while the sum is 37.

Adding to 81506121481 its reverse (18412160518), we get a palindrome (99918281999).

The spelling of 81506121481 in words is "eighty-one billion, five hundred six million, one hundred twenty-one thousand, four hundred eighty-one".