11307
that has 3 in it... we'll do 1131, to 111, ok so that would be 37, to 370, and it was 21 above that so 377, and then it was 3 down, so 3769 (x3) is what we're working with. Then looking at 7, from the left is 269, that's prime so 7 is out. and 11, from the left on the original, leaves 307 so no; 13 off the right side of 3769 (via 39) is 373, then 360, so no; looking at 17, we'll go from the left from 34 makes 369, which is just 123 (that's just 41) so no; looking at 19, from the right makes 375, 5 away from 38 so no; 23 can take 69 off, left with 37 and no; 29 off the right makes 374, in half is 187, not 29 (87 would be); only have to get up to just over 60 on this; checking 31 from the left leaves 669 or 223 which is itself prime so no; 37 knocks right off to 69 and no; 41 on the right brings you to 381, down to 34(0), not it; 43 can go via 301 on the right which makes 4070, 407 being the wrong distance from 430; 53 can use 901 on the right, makes 467, adding 53 again goes to 52 WOW close; doing 59 from the right makes 371, and then up to 43 so no; 61 and this will be the last one because 60 squared is 3600 and 67 squared will obviously be well on its way toward 4900 so 61 is really the only hope and if i've made no mistakes so far it would have to be squared which clearly would be the wrong answer because it doesn't end with 1, but we can check anyway on the right, goes up to 383 which is prime itself but if you don't believe that then just take away 183 (61's tripple) and you're left with 100 so 61 is out. Making the final answer 3769x3