Number of unconstrained walks on square lattice trapped after n steps.

Terms

a(0) =1a(1) =1a(2) =2a(3) =5a(4) =15a(5) =30a(6) =76a(7) =170a(8) =422a(9) =961a(10) =2339a(11) =5390a(12) =12977a(13) =30059a(14) =71918a(15) =167019a(16) =397691a(17) =924931a(18) =2194478a(19) =5107991a(20) =12085695a(21) =28143758a(22) =66442935a(23) =154759821a(24) =364706675a(25) =849562628