81812161656 has 24 divisors (see below), whose sum is σ = 221574604680. Its totient is φ = 27270720528.

The previous prime is 81812161637. The next prime is 81812161679. The reversal of 81812161656 is 65616121818.

81812161656 is a `hidden beast` number, since 8 + 1 + 8 + 1 + 21 + 616 + 5 + 6 = 666.

It is a tau number, because it is divible by the number of its divisors (24).

It is an alternating number because its digits alternate between even and odd.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 568139940 + ... + 568140083.

It is an arithmetic number, because the mean of its divisors is an integer number (9232275195).

Almost surely, 2^81812161656 is an apocalyptic number.

It is an amenable number.

81812161656 is an abundant number, since it is smaller than the sum of its proper divisors (139762443024).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

81812161656 is a wasteful number, since it uses less digits than its factorization.

81812161656 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1136280035 (or 1136280028 counting only the distinct ones).

The product of its digits is 138240, while the sum is 45.

The spelling of 81812161656 in words is "eighty-one billion, eight hundred twelve million, one hundred sixty-one thousand, six hundred fifty-six".