A026155 T(n,n-4), where T is the array in A026148.
1, 4, 16, 56, 189, 616, 1967, 6182, 19205, 59124, 180726, 549276, 1661646, 5007520, 15042722, 45068836, 134727499, 401991436, 1197519631, 3562523314, 10585937404, 31424706800, 93206486620, 276253350360, 818278951035, 2422518642516
Offset: 4
Keywords
Crossrefs
First differences of A026329.
Formula
Conjectures from Chai Wah Wu, Mar 23 2020: (Start)
a(n) = 12*a(n-1) - 53*a(n-2) + 90*a(n-3) + 26*a(n-4) - 256*a(n-5) + 160*a(n-6) + 224*a(n-7) - 203*a(n-8) - 84*a(n-9) + 77*a(n-10) + 14*a(n-11) - 7*a(n-12) for n > 15.
G.f.: x^4*(x - 1)^2*(x^6 - 6*x^5 - 13*x^4 + 8*x^3 + 8*x^2 - 6*x + 1)/((7*x^6 + 7*x^5 - 21*x^4 + 14*x^2 - 7*x + 1)*(x^6 - 3*x^5 - 5*x^4 + 8*x^3 + 4*x^2 - 5*x + 1)). (End)