Number of nX2 1..3 arrays containing at least one of each value, and all equal values connected.

Terms

a(0) =0a(1) =24a(2) =174a(3) =642a(4) =1716a(5) =3780a(6) =7314a(7) =12894a(8) =21192a(9) =32976a(10) =49110a(11) =70554a(12) =98364a(13) =133692a(14) =177786a(15) =231990a(16) =297744a(17) =376584a(18) =470142a(19) =580146a(20) =708420a(21) =856884a(22) =1027554a(23) =1222542a(24) =1444056a(25) =1694400a(26) =1975974a(27) =2291274a(28) =2642892a(29) =3033516