81521168291 has 4 divisors (see below), whose sum is σ = 81605472432. Its totient is φ = 81436864152.

The previous prime is 81521168233. The next prime is 81521168293. The reversal of 81521168291 is 19286112518.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 19286112518 = 2 ⋅9643056259.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-81521168291 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (81521168293) 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, 42150620 + ... + 42152553.

It is an arithmetic number, because the mean of its divisors is an integer number (20401368108).

Almost surely, 2^81521168291 is an apocalyptic number.

81521168291 is a deficient number, since it is larger than the sum of its proper divisors (84304141).

81521168291 is an equidigital number, since it uses as much as digits as its factorization.

81521168291 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 84304140.

The product of its digits is 69120, while the sum is 44.

The spelling of 81521168291 in words is "eighty-one billion, five hundred twenty-one million, one hundred sixty-eight thousand, two hundred ninety-one".