I think this seq (not in the OEIS) starts like this: C = 1,4,16,49,166,... We have: 1+2 divides 12 -> 12/3=4 4+5 divides 45 -> 45/9=5 16+17 divides 1617 -> 1617/33=49 49+50 divides 4950 -> 4950/99=50 166+167 divides 166167 -> 166167/333=499 ... Pattern? Best, É.