81900989 has 2 divisors, whose sum is σ = 81900990. Its totient is φ = 81900988.

The previous prime is 81900983. The next prime is 81901003. The reversal of 81900989 is 98900918.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 79798489 + 2102500 = 8933^2 + 1450^2 .

It is a cyclic number.

It is not a de Polignac number, because 81900989 - 2²⁰ = 80852413 is a prime.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81900983) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40950494 + 40950495.

It is an arithmetic number, because the mean of its divisors is an integer number (40950495).

Almost surely, 2^81900989 is an apocalyptic number.

It is an amenable number.

81900989 is a deficient number, since it is larger than the sum of its proper divisors (1).

81900989 is an equidigital number, since it uses as much as digits as its factorization.

81900989 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 46656, while the sum is 44.

The square root of 81900989 is about 9049.9165189520. The cubic root of 81900989 is about 434.2732198364.

The spelling of 81900989 in words is "eighty-one million, nine hundred thousand, nine hundred eighty-nine".