81521260731 has 16 divisors (see below), whose sum is σ = 120777887520. Its totient is φ = 54344964960.

The previous prime is 81521260703. The next prime is 81521260781. The reversal of 81521260731 is 13706212518.

81521260731 is a `hidden beast` number, since 8 + 1 + 5 + 2 + 12 + 607 + 31 = 666.

It is not a de Polignac number, because 81521260731 - 2¹⁴ = 81521244347 is a prime.

It is a super-2 number, since 2×81521260731² (a number of 23 digits) contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (81521260781) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 651561 + ... + 766533.

It is an arithmetic number, because the mean of its divisors is an integer number (7548617970).

Almost surely, 2^81521260731 is an apocalyptic number.

81521260731 is a deficient number, since it is larger than the sum of its proper divisors (39256626789).

81521260731 is a wasteful number, since it uses less digits than its factorization.

81521260731 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 141243 (or 141237 counting only the distinct ones).

The product of its (nonzero) digits is 20160, while the sum is 36.

The spelling of 81521260731 in words is "eighty-one billion, five hundred twenty-one million, two hundred sixty thousand, seven hundred thirty-one".