Найдите сумму первых двадцати членов последовательности заданной форму b=2n+1    

Веселая формула. Распишу подробно. b1 = 2*1 + 1 = 2 + 1 = 3 b2 = 2*2 + 1 = 4 + 1 = 5 b3 = 2*3 + 1 = 6 + 1 = 7 b4 = 2*4 + 1 = 8 + 1 = 9 b5 = 2*5 + 1 = 10 + 1 = 11 b6 = 2*6 + 1 = 12 + 1 = 13 b7 = 2*7 + 1 = 14 + 1 = 15 b8 = 2*8 + 1 = 16 + 1 = 17 b9 = 2*9 + 1 = 18 + 1 = 19 b10 = 2*10 + 1 = 20 + 1 = 21 b11 = 2*11 + 1 = 22 + 1 = 23 b12 = 2*12 + 1 = 24 + 1 = 25 b13 = 2*13 + 1 = 26 + 1 = 27 b14 = 2*14 + 1 = 28 + 1 = 29 b15 = 2*15 + 1 = 30 + 1 = 31 b16 = 2*16 + 1 = 32 + 1 = 33 b17 = 2*17 + 1 = 34 + 1 = 35 b18 = 2*18 + 1 = 36 + 1 = 37 b19 = 2*19 + 1 = 38 + 1 = 39 b20 = 2*20 + 1 = 40 + 1 = 41