Hello Math-Fun, This seq S is finite — but how many terms in it? And which is the last one? S = 1, 3, 4, 2, 41, 42, 21, 43, 44, 22, 45, etc. We are only interested in the cumulative sum Q which must be prime at every stage. The first term of Q is 13 — and this prime comes from the digits squeezing the 1st comma; the 2nd term of Q is 13 + 34 = 47 (prime) and 34 comes from the digits squeezing the 2nd comma; the 3rd term of Q is 47 + 42 = 89 (prime) and 42 comes from the digits squeezing the 3rd comma; the 4th term of Q is 89 + 24 = 113 (prime) and 24 comes from the digits squeezing the 4th comma; the 5th term of Q is 113 + 14 = 127 (prime) and 14 comes from the digits squeezing the 5th comma; etc. We don’t accept terms of S ending in 0 (zero). Best, É.