81891551889 has 27 divisors (see below), whose sum is σ = 137610188937. Its totient is φ = 46791738504.

The previous prime is 81891551879. The next prime is 81891551897. The reversal of 81891551889 is 98815519818.

The square root of 81891551889 is 286167.

It is a perfect power (a square), and thus also a powerful number.

It is not a de Polignac number, because 81891551889 - 2¹⁵ = 81891519121 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (63).

It is not an unprimeable number, because it can be changed into a prime (81891551879) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 26 ways as a sum of consecutive naturals, for example, 6002694 + ... + 6016320.

Almost surely, 2^81891551889 is an apocalyptic number.

81891551889 is the 286167-th square number.

81891551889 is the 143084-th centered octagonal number.

It is an amenable number.

81891551889 is a deficient number, since it is larger than the sum of its proper divisors (55718637048).

81891551889 is an frugal number, since it uses more digits than its factorization.

81891551889 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 27274 (or 13637 counting only the distinct ones).

The product of its digits is 8294400, while the sum is 63.

It can be divided in two parts, 8189155 and 1889, that added together give a square (8191044 = 2862²).

The spelling of 81891551889 in words is "eighty-one billion, eight hundred ninety-one million, five hundred fifty-one thousand, eight hundred eighty-nine".