81641637556 has 12 divisors (see below), whose sum is σ = 151277152068. Its totient is φ = 38419594112.

The previous prime is 81641637547. The next prime is 81641637589. The reversal of 81641637556 is 65573614618.

It can be written as a sum of positive squares in 2 ways, for example, as 40066427556 + 41575210000 = 200166^2 + 203900^2 .

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 600306091 + ... + 600306226.

It is an arithmetic number, because the mean of its divisors is an integer number (12606429339).

Almost surely, 2^81641637556 is an apocalyptic number.

It is an amenable number.

81641637556 is a deficient number, since it is larger than the sum of its proper divisors (69635514512).

81641637556 is a wasteful number, since it uses less digits than its factorization.

81641637556 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1200612338 (or 1200612336 counting only the distinct ones).

The product of its digits is 3628800, while the sum is 52.

The spelling of 81641637556 in words is "eighty-one billion, six hundred forty-one million, six hundred thirty-seven thousand, five hundred fifty-six".