81221075388 has 36 divisors (see below), whose sum is σ = 205643810008. Its totient is φ = 27029518560.

The previous prime is 81221075371. The next prime is 81221075447. The reversal of 81221075388 is 88357012218.

81221075388 is a `hidden beast` number, since 8 + 1 + 2 + 2 + 107 + 538 + 8 = 666.

It is a tau number, because it is divible by the number of its divisors (36).

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 1818178 + ... + 1862313.

Almost surely, 2^81221075388 is an apocalyptic number.

It is an amenable number.

81221075388 is an abundant number, since it is smaller than the sum of its proper divisors (124422734620).

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

81221075388 is a wasteful number, since it uses less digits than its factorization.

81221075388 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3681114 (or 3681109 counting only the distinct ones).

The product of its (nonzero) digits is 215040, while the sum is 45.

The spelling of 81221075388 in words is "eighty-one billion, two hundred twenty-one million, seventy-five thousand, three hundred eighty-eight".