81791406621 has 24 divisors (see below), whose sum is σ = 126959811264. Its totient is φ = 50554120320.

The previous prime is 81791406617. The next prime is 81791406623. The reversal of 81791406621 is 12660419718.

81791406621 is a `hidden beast` number, since 8 + 1 + 7 + 9 + 14 + 0 + 6 + 621 = 666.

It is not a de Polignac number, because 81791406621 - 2² = 81791406617 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81791406623) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 3979185 + ... + 3999686.

It is an arithmetic number, because the mean of its divisors is an integer number (5289992136).

Almost surely, 2^81791406621 is an apocalyptic number.

It is an amenable number.

81791406621 is a deficient number, since it is larger than the sum of its proper divisors (45168404643).

81791406621 is a wasteful number, since it uses less digits than its factorization.

81791406621 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7978961 (or 7978958 counting only the distinct ones).

The product of its (nonzero) digits is 145152, while the sum is 45.

The spelling of 81791406621 in words is "eighty-one billion, seven hundred ninety-one million, four hundred six thousand, six hundred twenty-one".