A population of 23.781 might be 23,781 or might be something larger, it just depends on what exact figure is actually being provided (since a decimal count makes no sense).

let 'p' represent the initial population (23.781)

let 'T' represent the new population

let 'r' represent the rate of change (1-0.023)

let 'y' represent the number of years (17)

the exponential equation we have is:

T = p*r^y

T = 23.781*(1-0.023)^17

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calculate exponential decrease

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T = 16.012

...so, the town's population is now 16.012 but no way of determining what units are intended