81900981 has 6 divisors (see below), whose sum is σ = 118301430. Its totient is φ = 54600648.

The previous prime is 81900971. The next prime is 81900983. The reversal of 81900981 is 18900918.

It can be written as a sum of positive squares in only one way, i.e., 70408881 + 11492100 = 8391^2 + 3390^2 .

It is not a de Polignac number, because 81900981 - 2²⁵ = 48346549 is a prime.

It is a super-2 number, since 2×81900981² = 13415541377524722, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81900983) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 4550046 + ... + 4550063.

It is an arithmetic number, because the mean of its divisors is an integer number (19716905).

Almost surely, 2^81900981 is an apocalyptic number.

It is an amenable number.

81900981 is a deficient number, since it is larger than the sum of its proper divisors (36400449).

81900981 is a wasteful number, since it uses less digits than its factorization.

81900981 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 9100115 (or 9100112 counting only the distinct ones).

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

The square root of 81900981 is about 9049.9160769589. The cubic root of 81900981 is about 434.2732056966.

The spelling of 81900981 in words is "eighty-one million, nine hundred thousand, nine hundred eighty-one".