hihi, all - oops - my program did not count sequences in which one of the terms was equal to the sum of the previous terms (< instead of <= in the loop condition 8-() anyway, here are the revised counts 1 chains of length 1 1 chains of length 2 2 chains of length 3 2 chains of length 4 4 chains of length 5 5 chains of length 6 7 chains of length 7 7 chains of length 8 24 chains of length 9 22 chains of length 10 29 chains of length 11 39 chains of length 12 67 chains of length 13 55 chains of length 14 386 chains of length 15 235 chains of length 16 312 chains of length 17 347 chains of length 18 451 chains of length 19 1319 chains of length 20 5320 chains of length 21 3220 chains of length 22 4489 chains of length 23 20237 chains of length 24 36580 chains of length 25 52875 chains of length 26 197103 chains of length 27 more soon, cal