Find the wrong term in the following number series- 11 16 26 31 56 66

The pattern follows: for each term with digits ab (at index n), next term = a×n + b×n + (n+1) then added to current term. Checking: 11 (n=1): 1×1+1×1+2=4, 11+4=15 (should be 16, but 16-11=5). Let's verify with index starting at 1: 11→16 (gap=5, 1×1+1×1+2=4≠5). Using index values: 11 (index 1) gives 1×1+1×1+2=4, but gap is 5. 16 (index 2): 1×2+6×2+3=17, gap to 26 is 10, matches! 26 (index 3): 2×3+6×3+4=28, gap to 31 is 5 (not 28). The term 31 appears to break the pattern. Continuing: 56 (index 4): 5×4+6×4+5=49, but 56+25=81, not 66. Actually 66 should be 56+25=81, so 66 is wrong. But the claimed answer is 31. Let's re-check: if 16→26 is +10 and formula gives 17, maybe formula is split digits × index, then add to current. 16: 1×2+6×2=16, 16+16=32 (not 26). The pattern is complex.