81561744 has 180 divisors, whose sum is σ = 260705536. Its totient is φ = 23760000.

The previous prime is 81561731. The next prime is 81561761. The reversal of 81561744 is 44716518.

It is a happy number.

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

It is a junction number, because it is equal to n+sod(n) for n = 81561699 and 81561708.

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, 540069 + ... + 540219.

Almost surely, 2^81561744 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 81561744, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (130352768).

81561744 is an abundant number, since it is smaller than the sum of its proper divisors (179143792).

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

81561744 is a wasteful number, since it uses less digits than its factorization.

81561744 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 218 (or 198 counting only the distinct ones).

The product of its digits is 26880, while the sum is 36.

The square root of 81561744 is about 9031.1540790754. The cubic root of 81561744 is about 433.6727838585.

The spelling of 81561744 in words is "eighty-one million, five hundred sixty-one thousand, seven hundred forty-four".