a(n) = n^4 - 2*n^3 + 3*n^2 - 2*n + 1, the Alexander polynomial for reef and granny knots.

Terms

a(0) =1a(1) =1a(2) =9a(3) =49a(4) =169a(5) =441a(6) =961a(7) =1849a(8) =3249a(9) =5329a(10) =8281a(11) =12321a(12) =17689a(13) =24649a(14) =33489a(15) =44521a(16) =58081a(17) =74529a(18) =94249a(19) =117649a(20) =145161a(21) =177241a(22) =214369a(23) =257049a(24) =305809a(25) =361201a(26) =423801a(27) =494209a(28) =573049a(29) =660969