81909193 has 2 divisors, whose sum is σ = 81909194. Its totient is φ = 81909192.

The previous prime is 81909173. The next prime is 81909227. The reversal of 81909193 is 39190918.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 79512889 + 2396304 = 8917^2 + 1548^2 .

It is a cyclic number.

It is not a de Polignac number, because 81909193 - 2¹⁷ = 81778121 is a prime.

It is a super-2 number, since 2×81909193² = 13418231795822498, which contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (81909173) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40954596 + 40954597.

It is an arithmetic number, because the mean of its divisors is an integer number (40954597).

Almost surely, 2^81909193 is an apocalyptic number.

It is an amenable number.

81909193 is a deficient number, since it is larger than the sum of its proper divisors (1).

81909193 is an equidigital number, since it uses as much as digits as its factorization.

81909193 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 17496, while the sum is 40.

The square root of 81909193 is about 9050.3697714513. The cubic root of 81909193 is about 434.2877196960.

The spelling of 81909193 in words is "eighty-one million, nine hundred nine thousand, one hundred ninety-three".