81951891 has 8 divisors (see below), whose sum is σ = 124879104. Its totient is φ = 46829640.

The previous prime is 81951889. The next prime is 81951911. The reversal of 81951891 is 19815918.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 81951891 - 2¹ = 81951889 is a prime.

It is a super-2 number, since 2×81951891² = 13432224876951762, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (81951811) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 1951215 + ... + 1951256.

It is an arithmetic number, because the mean of its divisors is an integer number (15609888).

Almost surely, 2^81951891 is an apocalyptic number.

81951891 is a deficient number, since it is larger than the sum of its proper divisors (42927213).

81951891 is a wasteful number, since it uses less digits than its factorization.

81951891 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3902481.

The product of its digits is 25920, while the sum is 42.

The square root of 81951891 is about 9052.7283732585. The cubic root of 81951891 is about 434.3631690858.

The spelling of 81951891 in words is "eighty-one million, nine hundred fifty-one thousand, eight hundred ninety-one".