Answer:
Step-by-step explanation:
3^(n-1) * (n(n+1)/2 = 20412
The n(n +1)/2 is a factorial which is defined for integers so we are looking for a whole number solution.
We could draw a graph manually or using software and get the solution where the graph cuts the x axis.
Also we could find the prime factors of 20412:
20412 = 2^2 * 3^6 * 7
and try substituting 2, 3 and 7 into the equation
Using this method we see that one solution is n = 7.
I could have tried n = 7 first because 3^n-1 = 3^6!!
