Triangle: r=23;l=7;m(r,l,n)=(r - l)*IdentityMatrix[n] + l*Table[1, {i, 1, n}, {j, 1, n}].

Terms

a(0) =1a(1) =23a(2) =-1a(3) =480a(4) =-46a(5) =1a(6) =9472a(7) =-1440a(8) =69a(9) =-1a(10) =180224a(11) =-37888a(12) =2880a(13) =-92a(14) =1a(15) =3342336a(16) =-901120a(17) =94720a(18) =-4800a(19) =115a(20) =-1a(21) =60817408a(22) =-20054016a(23) =2703360a(24) =-189440a(25) =7200a(26) =-138a(27) =1a(28) =1090519040a(29) =-425721856