: ▁▁ 3 2 1 ▁Prime ▁Search ▁▁ 3 2 1 ▁Prime ▁Search ▁is ▁a ▁continu ation ▁of ▁Paul ▁Under wood ' s ▁ 3 2 1 ▁Search ▁which ▁looked ▁for ▁pr imes ▁of ▁the ▁form ▁ 3   ·   2 n   −   1 . ▁Prime Grid ▁added ▁the ▁+ 1 ▁form ▁and ▁continues ▁the ▁search ▁up ▁to   n   =   2 5 M . ▁ ▁Pr imes ▁known ▁for ▁ 3   ·   2 n   +   1 ▁occur ▁at ▁the ▁following ▁n : ▁▁ 1 , ▁ 2 , ▁ 5 , ▁ 6 , ▁ 8 , ▁ 1 2 , ▁ 1 8 , ▁ 3 0 , ▁ 3 6 , ▁ 4 1 , ▁ 6 6 , ▁ 1 8 9 , ▁ 2 0 1 , ▁ 2 0 9 , ▁ 2 7 6 , ▁ 3 5 3 , ▁ 4 0 8 , ▁ 4 3 8 , ▁ 5 3 4 , ▁ 2 2 0 8 , ▁ 2 8 1 6 , ▁ 3 1 6 8 , ▁ 3 1 8 9 , ▁ 3 9 1 2 , ▁ 2 0 9 0 9 , ▁ 3 4 3 5 0 , ▁ 4 2 2 9 4 , ▁ 4 2 6 6 5 , ▁ 4 4 6 8 5 , ▁ 4 8 1 5 0 , ▁ 5 4 7 9 2 , ▁ 5 5