81521649101 has 4 divisors (see below), whose sum is σ = 81522359292. Its totient is φ = 81520938912.

The previous prime is 81521649061. The next prime is 81521649103. The reversal of 81521649101 is 10194612518.

It is a happy number.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length, and also an emirpimes, since its reverse is a distinct semiprime: 10194612518 = 2 ⋅5097306259.

It can be written as a sum of positive squares in 2 ways, for example, as 45252351076 + 36269298025 = 212726^2 + 190445^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-81521649101 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81521649103) 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, 139130 + ... + 427083.

It is an arithmetic number, because the mean of its divisors is an integer number (20380589823).

Almost surely, 2^81521649101 is an apocalyptic number.

It is an amenable number.

81521649101 is a deficient number, since it is larger than the sum of its proper divisors (710191).

81521649101 is a wasteful number, since it uses less digits than its factorization.

81521649101 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 710190.

The product of its (nonzero) digits is 17280, while the sum is 38.

The spelling of 81521649101 in words is "eighty-one billion, five hundred twenty-one million, six hundred forty-nine thousand, one hundred one".