81421791 has 24 divisors (see below), whose sum is σ = 120335616. Its totient is φ = 48565440.

The previous prime is 81421787. The next prime is 81421831. The reversal of 81421791 is 19712418.

It is not a de Polignac number, because 81421791 - 2² = 81421787 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (33).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81421391) 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, 175626 + ... + 176088.

It is an arithmetic number, because the mean of its divisors is an integer number (5013984).

Almost surely, 2^81421791 is an apocalyptic number.

81421791 is a deficient number, since it is larger than the sum of its proper divisors (38913825).

81421791 is a wasteful number, since it uses less digits than its factorization.

81421791 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 623 (or 550 counting only the distinct ones).

The product of its digits is 4032, while the sum is 33.

The square root of 81421791 is about 9023.4024070746. The cubic root of 81421791 is about 433.4245933368.

The spelling of 81421791 in words is "eighty-one million, four hundred twenty-one thousand, seven hundred ninety-one".