Find the odd man out.

Concept: In alphanumeric series where a letter sits between two digits, the two outer digits are often designed to concatenate into a number that equals the letter's position in the English alphabet (A = 1, B = 2, ..., Z = 26). To spot the odd one out, apply this rule to every item and find the one where it fails.

• 0A1: the outer digits 0 and 1 concatenate to 01, i.e., 1 — and A is the 1st letter, so the pattern holds.

• 1R8: the outer digits 1 and 8 concatenate to 18 — and R is the 18th letter, so the pattern holds.

• 1P6: the outer digits 1 and 6 concatenate to 16 — and P is the 16th letter, so the pattern holds.

• 2Y4: the outer digits 2 and 4 concatenate to 24 — but Y is the 25th letter, not the 24th, so the pattern breaks here.

Cross-check: three of the four items independently satisfy outer-digits = letter's alphabetical position; only 2Y4 fails that check, confirming it as the one that does not belong.

Answer: 2Y4 is the odd one out.