81891320 has 32 divisors (see below), whose sum is σ = 210578400. Its totient is φ = 28076928.

The previous prime is 81891287. The next prime is 81891361. The reversal of 81891320 is 2319818.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 145955 + ... + 146514.

It is an arithmetic number, because the mean of its divisors is an integer number (6580575).

Almost surely, 2^81891320 is an apocalyptic number.

It is an amenable number.

81891320 is an abundant number, since it is smaller than the sum of its proper divisors (128687080).

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

81891320 is a wasteful number, since it uses less digits than its factorization.

81891320 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 292487 (or 292483 counting only the distinct ones).

The product of its (nonzero) digits is 3456, while the sum is 32.

The square root of 81891320 is about 9049.3822993617. The cubic root of 81891320 is about 434.2561294729.

The spelling of 81891320 in words is "eighty-one million, eight hundred ninety-one thousand, three hundred twenty".