81561312 has 144 divisors (see below), whose sum is σ = 276756480. Its totient is φ = 22277376.

The previous prime is 81561307. The next prime is 81561317. The reversal of 81561312 is 21316518.

It is an interprime number because it is at equal distance from previous prime (81561307) and next prime (81561317).

It is a tau number, because it is divible by the number of its divisors (144).

It is a super-2 number, since 2×81561312² = 13304495230322688, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81561317) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 45489 + ... + 47247.

It is an arithmetic number, because the mean of its divisors is an integer number (1921920).

Almost surely, 2^81561312 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 81561312, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (138378240).

81561312 is an abundant number, since it is smaller than the sum of its proper divisors (195195168).

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

81561312 is a wasteful number, since it uses less digits than its factorization.

81561312 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1805 (or 1794 counting only the distinct ones).

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

The square root of 81561312 is about 9031.1301618347. The cubic root of 81561312 is about 433.6720181933.

The spelling of 81561312 in words is "eighty-one million, five hundred sixty-one thousand, three hundred twelve".