81817402509 has 20 divisors (see below), whose sum is σ = 122299946076. Its totient is φ = 54509728896.

The previous prime is 81817402507. The next prime is 81817402543. The reversal of 81817402509 is 90520471818.

It can be written as a sum of positive squares in 2 ways, for example, as 14399280009 + 67418122500 = 119997^2 + 259650^2 .

It is not a de Polignac number, because 81817402509 - 2¹ = 81817402507 is a prime.

It is a Smith number, since the sum of its digits (45) coincides with the sum of the digits of its prime factors.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81817402507) by changing a digit.

It is a polite number, since it can be written in 19 ways as a sum of consecutive naturals, for example, 199414 + ... + 450999.

Almost surely, 2^81817402509 is an apocalyptic number.

It is an amenable number.

81817402509 is a deficient number, since it is larger than the sum of its proper divisors (40482543567).

81817402509 is a wasteful number, since it uses less digits than its factorization.

81817402509 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 651978 (or 651969 counting only the distinct ones).

The product of its (nonzero) digits is 161280, while the sum is 45.

The spelling of 81817402509 in words is "eighty-one billion, eight hundred seventeen million, four hundred two thousand, five hundred nine".