81897620 has 72 divisors (see below), whose sum is σ = 201565224. Its totient is φ = 27869184.

The previous prime is 81897617. The next prime is 81897661. The reversal of 81897620 is 2679818.

It can be written as a sum of positive squares in 4 ways, for example, as 103684 + 81793936 = 322^2 + 9044^2 .

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 188924 + ... + 189356.

It is an arithmetic number, because the mean of its divisors is an integer number (2799517).

Almost surely, 2^81897620 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 81897620, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (100782612).

81897620 is an abundant number, since it is smaller than the sum of its proper divisors (119667604).

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

81897620 is a wasteful number, since it uses less digits than its factorization.

81897620 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 649 (or 640 counting only the distinct ones).

The product of its (nonzero) digits is 48384, while the sum is 41.

The square root of 81897620 is about 9049.7303827241. The cubic root of 81897620 is about 434.2672651401.

The spelling of 81897620 in words is "eighty-one million, eight hundred ninety-seven thousand, six hundred twenty".