81751644 has 72 divisors (see below), whose sum is σ = 223663440. Its totient is φ = 25028352.

The previous prime is 81751613. The next prime is 81751687. The reversal of 81751644 is 44615718.

81751644 = T₈₇ + T₈₈ + ... + T₇₈₈.

It is a happy number.

81751644 is a `hidden beast` number, since 8 + 1 + 7 + 5 + 1 + 644 = 666.

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 = 81751599 and 81751608.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 143392 + ... + 143960.

Almost surely, 2^81751644 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 81751644, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (111831720).

81751644 is an abundant number, since it is smaller than the sum of its proper divisors (141911796).

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

81751644 is a wasteful number, since it uses less digits than its factorization.

81751644 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 899 (or 894 counting only the distinct ones).

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

The square root of 81751644 is about 9041.6615729632. The cubic root of 81751644 is about 434.0090960597.

The spelling of 81751644 in words is "eighty-one million, seven hundred fifty-one thousand, six hundred forty-four".