Number of n-step self-avoiding paths on quadrant grid starting at quadrant origin.

Terms

a(0) =1a(1) =2a(2) =4a(3) =10a(4) =24a(5) =60a(6) =146a(7) =366a(8) =912a(9) =2302a(10) =5800a(11) =14722a(12) =37368a(13) =95304a(14) =243168a(15) =622518a(16) =1594622a(17) =4094768a(18) =10521384a(19) =27085436a(20) =69768478a(21) =179982688a(22) =464564220a(23) =1200563864a(24) =3104192722a(25) =8034256412a(26) =20803994184a(27) =53915334890a(28) =139785953076a(29) =362681515714