81661320 has 96 divisors (see below), whose sum is σ = 285831000. Its totient is φ = 20100096.

The previous prime is 81661301. The next prime is 81661379. The reversal of 81661320 is 2316618.

It can be written as a sum of positive squares in 4 ways, for example, as 74338884 + 7322436 = 8622^2 + 2706^2 .

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, 4045 + ... + 13404.

Almost surely, 2^81661320 is an apocalyptic number.

It is an amenable number.

81661320 is an abundant number, since it is smaller than the sum of its proper divisors (204169680).

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

81661320 is a wasteful number, since it uses less digits than its factorization.

81661320 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 17479 (or 17472 counting only the distinct ones).

The product of its (nonzero) digits is 1728, while the sum is 27.

The square root of 81661320 is about 9036.6653141521. The cubic root of 81661320 is about 433.8491976084.

Adding to 81661320 its reverse (2316618), we get a palindrome (83977938).

The spelling of 81661320 in words is "eighty-one million, six hundred sixty-one thousand, three hundred twenty".