Identify the next term of the series 1, 2, 6, 21, 88, ?

Explanation

1. 01

   Try a changing multiplier with a matching addition: $1 \times 1 + 1 = 2$, $2 \times 2 + 2 = 6$, $6 \times 3 + 3 = 21$, $21 \times 4 + 4 = 88$.

2. 02

   The next step is $\times 5 + 5$: $88 \times 5 + 5 = 440 + 5 = 445$.