81371664 has 120 divisors (see below), whose sum is σ = 253948032. Its totient is φ = 24111360.

The previous prime is 81371663. The next prime is 81371669. The reversal of 81371664 is 46617318.

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

It is not an unprimeable number, because it can be changed into a prime (81371663) 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, 73902 + ... + 74994.

Almost surely, 2^81371664 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 81371664, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (126974016).

81371664 is an abundant number, since it is smaller than the sum of its proper divisors (172576368).

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

81371664 is a wasteful number, since it uses less digits than its factorization.

81371664 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1165 (or 1156 counting only the distinct ones).

The product of its digits is 24192, while the sum is 36.

The square root of 81371664 is about 9020.6243686344. The cubic root of 81371664 is about 433.3356297051.

It can be divided in two parts, 8137 and 1664, that added together give a square (9801 = 99²).

The spelling of 81371664 in words is "eighty-one million, three hundred seventy-one thousand, six hundred sixty-four".