81621900 has 108 divisors (see below), whose sum is σ = 258967800. Its totient is φ = 21500160.

The previous prime is 81621899. The next prime is 81621907. The reversal of 81621900 is 912618.

It is a super-2 number, since 2×81621900² = 13324269119220000, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81621907) by changing a digit.

It is a polite number, since it can be written in 35 ways as a sum of consecutive naturals, for example, 79591 + ... + 80609.

It is an arithmetic number, because the mean of its divisors is an integer number (2397850).

Almost surely, 2^81621900 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 81621900, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (129483900).

81621900 is an abundant number, since it is smaller than the sum of its proper divisors (177345900).

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

81621900 is a wasteful number, since it uses less digits than its factorization.

81621900 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1128 (or 1118 counting only the distinct ones).

The product of its (nonzero) digits is 864, while the sum is 27.

The square root of 81621900 is about 9034.4839365622. The cubic root of 81621900 is about 433.7793763514.

The spelling of 81621900 in words is "eighty-one million, six hundred twenty-one thousand, nine hundred".