Coefficient of x^n in the expansion of ( (1-x+x^3) / (1-x) )^(2*n).

Terms

a(0) =1a(1) =0a(2) =0a(3) =6a(4) =8a(5) =10a(6) =78a(7) =196a(8) =376a(9) =1446a(10) =4390a(11) =10648a(12) =32822a(13) =101426a(14) =276976a(15) =808666a(16) =2449528a(17) =7046942a(18) =20491458a(19) =61124482a(20) =179376718a(21) =525065722a(22) =1556298700a(23) =4598892274a(24) =13546834582a(25) =40109057710a(26) =118836735758a(27) =351539306142