81991019 has 8 divisors (see below), whose sum is σ = 90577920. Its totient is φ = 73593000.

The previous prime is 81990991. The next prime is 81991027. The reversal of 81991019 is 91019918.

It is a happy number.

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

It is a cyclic number.

It is not a de Polignac number, because 81991019 - 2⁸ = 81990763 is a prime.

It is a super-2 number, since 2×81991019² = 13445054393316722, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (81991319) 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, 46307 + ... + 48044.

It is an arithmetic number, because the mean of its divisors is an integer number (11322240).

Almost surely, 2^81991019 is an apocalyptic number.

81991019 is a deficient number, since it is larger than the sum of its proper divisors (8586901).

81991019 is a wasteful number, since it uses less digits than its factorization.

81991019 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 94441.

The product of its (nonzero) digits is 5832, while the sum is 38.

The square root of 81991019 is about 9054.8892317907. The cubic root of 81991019 is about 434.4322871083.

The spelling of 81991019 in words is "eighty-one million, nine hundred ninety-one thousand, nineteen".