A027261 a(n) = Sum_{k=0..2n} (k+1) * A025177(n, k).
1, 4, 18, 72, 270, 972, 3402, 11664, 39366, 131220, 433026, 1417176, 4605822, 14880348, 47829690, 153055008, 487862838, 1549681956, 4907326194, 15496819560, 48814981614, 153418513644, 481176247338, 1506290861232, 4707158941350, 14686335897012, 45753584909922
Offset: 0
Keywords
Formula
a(n) = 2(n+1)*3^(n-1), for n>1 (conjectured). - Ralf Stephan, Feb 02 2004
From Colin Barker, Jul 28 2012: (Start)
Conjecture: a(n) = 6*a(n-1)-9*a(n-2), for n>3.
G.f.: (1-9*x^2+18*x^3)/(1-3*x)^2. (End)
Extensions
a(1) corrected and more terms from Sean A. Irvine, Oct 26 2019