81521175313 has 2 divisors, whose sum is σ = 81521175314. Its totient is φ = 81521175312.

The previous prime is 81521175311. The next prime is 81521175343. The reversal of 81521175313 is 31357112518.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 57968748289 + 23552427024 = 240767^2 + 153468^2 .

It is a cyclic number.

It is not a de Polignac number, because 81521175313 - 2¹ = 81521175311 is a prime.

Together with 81521175311, it forms a pair of twin primes.

It is not a weakly prime, because it can be changed into another prime (81521175311) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40760587656 + 40760587657.

It is an arithmetic number, because the mean of its divisors is an integer number (40760587657).

Almost surely, 2^81521175313 is an apocalyptic number.

It is an amenable number.

81521175313 is a deficient number, since it is larger than the sum of its proper divisors (1).

81521175313 is an equidigital number, since it uses as much as digits as its factorization.

81521175313 is an evil number, because the sum of its binary digits is even.

The product of its digits is 25200, while the sum is 37.

The spelling of 81521175313 in words is "eighty-one billion, five hundred twenty-one million, one hundred seventy-five thousand, three hundred thirteen".