Illustration for the tootkpick sequence A139250. A vertical toothpick is represented as | | A horizontal toothpick is represented as - - Note in each case the space between the two dashes. Therefore - - - - represents two adjacent toothpicks. a(0) = 0 a(1) = 1 | | a(2) = 3 - - | | - - a(3) = 7 | | - - | | | | | | - - | | a(4) = 11 - - - - | | - - | | | | | | - - | | - - - - a(5) = 15 | | - - - - | | | | - - | | | | | | - - | | | | - - - - | | a(6) = 23 - - - - | | - - - - | | | | - - - - - - | | | | | | - - - - - - | | | | - - - - | | - - - - a(7) = 35 | | | | - - - - | | | | | | - - - - | | | | | | - - - - - - | | | | | | | | | | - - - - - - | | | | | | - - - - | | | | | | - - - - | | | | a(8) = 43 - - - - - - - - | | | | - - - - | | | | | | - - - - | | | | | | - - - - - - | | | | | | | | | | - - - - - - | | | | | | - - - - | | | | | | - - - - | | | | - - - - - - - - a(9) = 47 | | - - - - - - - - | | | | | | - - - - | | | | | | - - - - | | | | | | - - - - - - | | | | | | | | | | - - - - - - | | | | | | - - - - | | | | | | - - - - | | | | | | - - - - - - - - | |