81561800 has 48 divisors (see below), whose sum is σ = 190703940. Its totient is φ = 32440320.

The previous prime is 81561793. The next prime is 81561803. The reversal of 81561800 is 816518.

It can be written as a sum of positive squares in 6 ways, for example, as 1387684 + 80174116 = 1178^2 + 8954^2 .

It is not an unprimeable number, because it can be changed into a prime (81561803) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 37544 + ... + 39656.

Almost surely, 2^81561800 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 81561800, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (95351970).

81561800 is an abundant number, since it is smaller than the sum of its proper divisors (109142140).

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

81561800 is a wasteful number, since it uses less digits than its factorization.

81561800 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2322 (or 2313 counting only the distinct ones).

The product of its (nonzero) digits is 1920, while the sum is 29.

The square root of 81561800 is about 9031.1571794538. The cubic root of 81561800 is about 433.6728831112.

The spelling of 81561800 in words is "eighty-one million, five hundred sixty-one thousand, eight hundred".