81505668746401 has 27 divisors (see below), whose sum is σ = 83475632879667. Its totient is φ = 79581890813040.

The previous prime is 81505668746351. The next prime is 81505668746407. The reversal of 81505668746401 is 10464786650518.

The square root of 81505668746401 is 9028049.

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., 53673924410001 + 27831744336400 = 7326249^2 + 5275580^2 .

It is not a de Polignac number, because 81505668746401 - 2³³ = 81497078811809 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 81505668746401.

It is not an unprimeable number, because it can be changed into a prime (81505668746407) by changing a digit.

It is a polite number, since it can be written in 26 ways as a sum of consecutive naturals, for example, 76819668411 + ... + 76819669471.

Almost surely, 2^{81505668746401} is an apocalyptic number.

81505668746401 is the 9028049-th square number.

81505668746401 is the 4514025-th centered octagonal number.

It is an amenable number.

81505668746401 is a deficient number, since it is larger than the sum of its proper divisors (1969964133266).

81505668746401 is an frugal number, since it uses more digits than its factorization.

81505668746401 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2510 (or 1255 counting only the distinct ones).

The product of its (nonzero) digits is 38707200, while the sum is 61.

The spelling of 81505668746401 in words is "eighty-one trillion, five hundred five billion, six hundred sixty-eight million, seven hundred forty-six thousand, four hundred one".