81981900 has 486 divisors, whose sum is σ = 353110212. Its totient is φ = 15724800.

The previous prime is 81981883. The next prime is 81981901. The reversal of 81981900 is 918918.

It is a super-2 number, since 2×81981900² = 13442063855220000, which contains 22 as substring.

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 (81981901) by changing a digit.

It is a polite number, since it can be written in 161 ways as a sum of consecutive naturals, for example, 6306294 + ... + 6306306.

Almost surely, 2^81981900 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 81981900, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (176555106).

81981900 is an abundant number, since it is smaller than the sum of its proper divisors (271128312).

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

81981900 is a wasteful number, since it uses less digits than its factorization.

81981900 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 71 (or 41 counting only the distinct ones).

The product of its (nonzero) digits is 5184, while the sum is 36.

The square root of 81981900 is about 9054.3856776702. The cubic root of 81981900 is about 434.4161807308.

It can be divided in two parts, 819 and 81900, that multiplied together give a square (67076100 = 8190²).

The spelling of 81981900 in words is "eighty-one million, nine hundred eighty-one thousand, nine hundred".