81521667128 has 64 divisors (see below), whose sum is σ = 176999217120. Its totient is φ = 34788352000.

The previous prime is 81521667109. The next prime is 81521667133. The reversal of 81521667128 is 82176612518.

It is a super-2 number, since 2×81521667128² (a number of 23 digits) contains 22 as substring.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 531950 + ... + 667842.

Almost surely, 2^81521667128 is an apocalyptic number.

81521667128 is a gapful number since it is divisible by the number (88) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 81521667128, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (88499608560).

81521667128 is an abundant number, since it is smaller than the sum of its proper divisors (95477549992).

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

81521667128 is a wasteful number, since it uses less digits than its factorization.

81521667128 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 136328 (or 136324 counting only the distinct ones).

The product of its digits is 322560, while the sum is 47.

The spelling of 81521667128 in words is "eighty-one billion, five hundred twenty-one million, six hundred sixty-seven thousand, one hundred twenty-eight".