What should come next in the sequence that begins 3 5 10 17 29 48?

The rule being used here is probably a recursive one: xn+2 = xn + xn+1 + 2 For instance, 48 = 17 + 29 + 2. Thus the nextnumber is: 29 + 48 + 2 = 79 And the series can be extended indefinitely in both directions, if we like: ...-39, 21, -16, 7, -7, 2, -3, 1, 0, 3, 5, 10, 17, 29, 48, 79, 129, 210, 341, 553...