$n \ k$ $a_1 \ a_2 \ \cdots \ a_n$
3 1 1 2 3
3You can make 3 patterns: $b = \{ 1 \}, \{ 2, 3 \}, \{ 3, 2 \}$
3 10 8 7 5
6You can make 6 patterns: $b = \{ 5, 7, 8 \}, \{ 5, 8, 7 \}, \{ 7, 5, 8 \}, \{ 7, 8, 5 \}, \{ 8, 5, 7 \}, \{ 8, 7, 5 \}$.
25 127 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 105 110 115 120 125
235924722
Please output answer mod $1,000,000,007$.