81581400 has 144 divisors (see below), whose sum is σ = 278843760. Its totient is φ = 21369600.

The previous prime is 81581399. The next prime is 81581413. The reversal of 81581400 is 418518.

81581400 is a `hidden beast` number, since 81 + 581 + 4 + 0 + 0 = 666.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 35 ways as a sum of consecutive naturals, for example, 109429 + ... + 110171.

It is an arithmetic number, because the mean of its divisors is an integer number (1936415).

Almost surely, 2^81581400 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 81581400, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (139421880).

81581400 is an abundant number, since it is smaller than the sum of its proper divisors (197262360).

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

81581400 is a wasteful number, since it uses less digits than its factorization.

81581400 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 826 (or 814 counting only the distinct ones).

The product of its (nonzero) digits is 1280, while the sum is 27.

The square root of 81581400 is about 9032.2422465299. The cubic root of 81581400 is about 433.7076187666.

Adding to 81581400 its reverse (418518), we get a palindrome (81999918).

It can be divided in two parts, 815 and 81400, that added together give a triangular number (82215 = T₄₀₅).

The spelling of 81581400 in words is "eighty-one million, five hundred eighty-one thousand, four hundred".