Number of n X n arrays of squares of integers with every 2X2 subblock summing to 18.

Terms

a(0) =30a(1) =78a(2) =166a(3) =342a(4) =678a(5) =1350a(6) =2662a(7) =5286a(8) =10470a(9) =20838a(10) =41446a(11) =82662a(12) =164838a(13) =329190a(14) =657382a(15) =1313766a(16) =2625510a(17) =5248998a(18) =10493926a(19) =20983782a(20) =41959398a(21) =83910630a(22) =167804902a(23) =335593446a(24) =671154150a(25) =1342275558