81561370646 has 8 divisors (see below), whose sum is σ = 139819492560. Its totient is φ = 34954873128.

The previous prime is 81561370637. The next prime is 81561370663. The reversal of 81561370646 is 64607316518.

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

It is a self number, because there is not a number n which added to its sum of digits gives 81561370646.

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, 2912906081 + ... + 2912906108.

It is an arithmetic number, because the mean of its divisors is an integer number (17477436570).

Almost surely, 2^81561370646 is an apocalyptic number.

81561370646 is a deficient number, since it is larger than the sum of its proper divisors (58258121914).

81561370646 is a wasteful number, since it uses less digits than its factorization.

81561370646 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5825812198.

The product of its (nonzero) digits is 725760, while the sum is 47.

The spelling of 81561370646 in words is "eighty-one billion, five hundred sixty-one million, three hundred seventy thousand, six hundred forty-six".