81313521 has 8 divisors (see below), whose sum is σ = 114124320. Its totient is φ = 51355872.

The previous prime is 81313513. The next prime is 81313543. The reversal of 81313521 is 12531318.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 81313521 - 2³ = 81313513 is a prime.

It is a super-2 number, since 2×81313521² = 13223777394834882, which contains 22 as substring.

It is a junction number, because it is equal to n+sod(n) for n = 81313491 and 81313500.

It is not an unprimeable number, because it can be changed into a prime (81313511) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 713220 + ... + 713333.

It is an arithmetic number, because the mean of its divisors is an integer number (14265540).

Almost surely, 2^81313521 is an apocalyptic number.

It is an amenable number.

81313521 is a deficient number, since it is larger than the sum of its proper divisors (32810799).

81313521 is a wasteful number, since it uses less digits than its factorization.

81313521 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1426575.

The product of its digits is 720, while the sum is 24.

The square root of 81313521 is about 9017.4010113779. The cubic root of 81313521 is about 433.2323937805.

Adding to 81313521 its reverse (12531318), we get a palindrome (93844839).

The spelling of 81313521 in words is "eighty-one million, three hundred thirteen thousand, five hundred twenty-one".