81559735942921 has 4 divisors (see below), whose sum is σ = 81973744755012. Its totient is φ = 81145727130832.

The previous prime is 81559735942891. The next prime is 81559735942931. The reversal of 81559735942921 is 12924953795518.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 80279808010000 + 1279927932921 = 8959900^2 + 1131339^2 .

It is a cyclic number.

It is not a de Polignac number, because 81559735942921 - 2³³ = 81551146008329 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (81559735942931) 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, 207004405750 + ... + 207004406143.

It is an arithmetic number, because the mean of its divisors is an integer number (20493436188753).

Almost surely, 2^{81559735942921} is an apocalyptic number.

It is an amenable number.

81559735942921 is a deficient number, since it is larger than the sum of its proper divisors (414008812091).

81559735942921 is a wasteful number, since it uses less digits than its factorization.

81559735942921 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 414008812090.

The product of its digits is 244944000, while the sum is 70.

The spelling of 81559735942921 in words is "eighty-one trillion, five hundred fifty-nine billion, seven hundred thirty-five million, nine hundred forty-two thousand, nine hundred twenty-one".