81809280 has 192 divisors, whose sum is σ = 323013600. Its totient is φ = 18690048.

The previous prime is 81809251. The next prime is 81809291. The reversal of 81809280 is 8290818.

It is a tau number, because it is divible by the number of its divisors (192).

It is a Harshad number since it is a multiple of its sum of digits (36).

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 39306 + ... + 41334.

Almost surely, 2^81809280 is an apocalyptic number.

81809280 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 81809280, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (161506800).

81809280 is an abundant number, since it is smaller than the sum of its proper divisors (241204320).

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

81809280 is a wasteful number, since it uses less digits than its factorization.

81809280 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2061 (or 2046 counting only the distinct ones).

The product of its (nonzero) digits is 9216, while the sum is 36.

The square root of 81809280 is about 9044.8482574336. The cubic root of 81809280 is about 434.1110661682. Note that the first 3 decimals are identical.

The spelling of 81809280 in words is "eighty-one million, eight hundred nine thousand, two hundred eighty".