81561600 has 288 divisors, whose sum is σ = 304668000. Its totient is φ = 21381120.

The previous prime is 81561551. The next prime is 81561629. The reversal of 81561600 is 616518.

81561600 is a `hidden beast` number, since 8 + 1 + 56 + 1 + 600 = 666.

It is a tau number, because it is divible by the number of its divisors (288).

It is a Harshad number since it is a multiple of its sum of digits (27).

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, 1382371 + ... + 1382429.

It is an arithmetic number, because the mean of its divisors is an integer number (1057875).

Almost surely, 2^81561600 is an apocalyptic number.

81561600 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 81561600, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (152334000).

81561600 is an abundant number, since it is smaller than the sum of its proper divisors (223106400).

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

81561600 is a wasteful number, since it uses less digits than its factorization.

81561600 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 100 (or 69 counting only the distinct ones).

The product of its (nonzero) digits is 1440, while the sum is 27.

The square root of 81561600 is about 9031.1461066689. The cubic root of 81561600 is about 433.6725286371.

The spelling of 81561600 in words is "eighty-one million, five hundred sixty-one thousand, six hundred".