81537691217 has 8 divisors (see below), whose sum is σ = 82605949800. Its totient is φ = 80475254784.

The previous prime is 81537691187. The next prime is 81537691231. The reversal of 81537691217 is 71219673518.

It is a happy number.

It can be written as a sum of positive squares in 4 ways, for example, as 34983587521 + 46554103696 = 187039^2 + 215764^2 .

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

It is a cyclic number.

It is not a de Polignac number, because 81537691217 - 2⁶ = 81537691153 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (81537691267) 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, 1427342 + ... + 1483367.

It is an arithmetic number, because the mean of its divisors is an integer number (10325743725).

Almost surely, 2^81537691217 is an apocalyptic number.

It is an amenable number.

81537691217 is a deficient number, since it is larger than the sum of its proper divisors (1068258583).

81537691217 is a wasteful number, since it uses less digits than its factorization.

81537691217 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2911075.

The product of its digits is 635040, while the sum is 50.

The spelling of 81537691217 in words is "eighty-one billion, five hundred thirty-seven million, six hundred ninety-one thousand, two hundred seventeen".