248,4816,51020

The sequence is generated by starting with a number, then concatenating its double and quadruple. The starting numbers follow a pattern of alternating between multiplying by 2 and adding 1:

1. 2 → 2, 4 (2×2), 8 (2×4) → 248

2. 4 → 4, 8 (4×2), 16 (4×4) → 4816

3. 5 (4+1) → 5, 10 (5×2), 20 (5×4) → 51020

4. 10 (5×2) → 10, 20, 40 → 102040

Next number: 102040

Pattern: Start with 2; alternate between ×2 and +1 for the starting number, then concatenate with its double and quadruple.