81621590091 has 4 divisors (see below), whose sum is σ = 108828786792. Its totient is φ = 54414393392.

The previous prime is 81621590041. The next prime is 81621590107. The reversal of 81621590091 is 19009512618.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 81621590091 - 2¹⁰ = 81621589067 is a prime.

It is not an unprimeable number, because it can be changed into a prime (81621590041) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 13603598346 + ... + 13603598351.

It is an arithmetic number, because the mean of its divisors is an integer number (27207196698).

Almost surely, 2^81621590091 is an apocalyptic number.

81621590091 is a deficient number, since it is larger than the sum of its proper divisors (27207196701).

81621590091 is a wasteful number, since it uses less digits than its factorization.

81621590091 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 27207196700.

The product of its (nonzero) digits is 38880, while the sum is 42.

The spelling of 81621590091 in words is "eighty-one billion, six hundred twenty-one million, five hundred ninety thousand, ninety-one".