81191890 has 32 divisors (see below), whose sum is σ = 161236656. Its totient is φ = 29245440.

The previous prime is 81191867. The next prime is 81191897. The reversal of 81191890 is 9819118.

It is a happy number.

It can be written as a sum of positive squares in 8 ways, for example, as 173889 + 81018001 = 417^2 + 9001^2 .

It is not an unprimeable number, because it can be changed into a prime (81191897) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 2287 + ... + 12946.

Almost surely, 2^81191890 is an apocalyptic number.

81191890 is a deficient number, since it is larger than the sum of its proper divisors (80044766).

81191890 is a wasteful number, since it uses less digits than its factorization.

81191890 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 15294.

The product of its (nonzero) digits is 5184, while the sum is 37.

The square root of 81191890 is about 9010.6542492762. The cubic root of 81191890 is about 433.0162723432.

The spelling of 81191890 in words is "eighty-one million, one hundred ninety-one thousand, eight hundred ninety".