Difference between two consecutive squares enclosing 3^(2n+1).

Terms

a(0) =3a(1) =11a(2) =31a(3) =93a(4) =281a(5) =841a(6) =2525a(7) =7575a(8) =22727a(9) =68183a(10) =204551a(11) =613655a(12) =1840965a(13) =5522897a(14) =16568691a(15) =49706071a(16) =149118215a(17) =447354647a(18) =1342063941a(19) =4026191825a(20) =12078575475a(21) =36235726425a(22) =108707179277a(23) =326121537829a(24) =978364613487