Q: can you finish prime factoring 1021
A: i think i left off after 19. next, check 23, we can use the triple. add 69 is 1090, drop the zero, 109 which i happen to know is prime (first decade of the 3 digits is prime-stuffed, i.e. 101, 103, 107, 109 are all prime) so therefore 23 is out. next check 29, add 29 is 1050, 105, double it is 210, drop the zero, 21, not a mult of 29. 29 is out. keep in mind we only have to go up to the square root of 1021 as long as we check thoroughly. 31 squared is 961, and 40 squared is 1600 so 37 squared is already gonna be too high. so 31 would be the last number we need to check. 1021 minus 31 is 990, drop the zero 99, clearly not a mult of 31. congratulations, 1021 is prime