37991

Work out 2n+3n for some different odd values of n.
What do you notice?
2n
1 2
3 8
5 32
2 and 8
2 and 8 are even because 2n equations always end in an even number and you can’t multiply a number by 2 and end up with an odd number.
3n
1 3
3 27
5 243
3 and 7
3 and 5 are odd as if you multiply and odd number by another odd number it as always ends up as an odd number. In our case 3 is being multiplied by 1, 3 and 5. I believe this because 3x3x3=27 and 7x3x3=63. So therefore it would continue forever.
2n+3n
1+1 5
3+3 35
5+5 275
5
The numbers always end in 5 as 2+3 is 5 and 8+7 is 15 ends in a 5 so it always ends in a 5.
So in conclusion all the odd n numbers like 23+33 end in 5 as 2+3 and 8+7 always end in 5.