81990904320 has 480 divisors, whose sum is σ = 315409723200. Its totient is φ = 20179501056.

The previous prime is 81990904313. The next prime is 81990904349. The reversal of 81990904320 is 2340909918.

It is a tau number, because it is divible by the number of its divisors (480).

It is a super-2 number, since 2×81990904320² (a number of 23 digits) contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (45).

It is an unprimeable number.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 11677771 + ... + 11684789.

It is an arithmetic number, because the mean of its divisors is an integer number (657103590).

Almost surely, 2^81990904320 is an apocalyptic number.

81990904320 is a gapful number since it is divisible by the number (80) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 81990904320, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (157704861600).

81990904320 is an abundant number, since it is smaller than the sum of its proper divisors (233418818880).

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

81990904320 is a wasteful number, since it uses less digits than its factorization.

81990904320 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7077 (or 7042 counting only the distinct ones).

The product of its (nonzero) digits is 139968, while the sum is 45.

It can be divided in two parts, 81990 and 904320, that added together give a triangular number (986310 = T₁₄₀₄).

The spelling of 81990904320 in words is "eighty-one billion, nine hundred ninety million, nine hundred four thousand, three hundred twenty".