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A192377
Coefficient of x in the reduction by x^2->x+2 of the polynomial p(n,x) defined below in Comments.
3
0, 2, 4, 20, 68, 262, 968, 3624, 13512, 50442, 188236, 702524, 2621836, 9784846, 36517520, 136285264, 508623504, 1898208786, 7084211604, 26438637668, 98670339028, 368242718486, 1374300534872, 5128959421048, 19141537149272, 71437189176090
OFFSET
1,2
COMMENTS
The polynomial p(n,x) is defined by ((x+d)^n - (x-d)^n)/(2d), where d=sqrt(x+1). A192377=2*A192378. For an introduction to reductions of polynomials by substitutions such as x^2->x+1, see A192232.
FORMULA
a(n) = 2*a(n-1) + 6*a(n-2) + 2*a(n-3) - a(n-4). - Colin Barker, Dec 09 2012
G.f.: 2*x^2 / ((x+1)^2*(x^2-4*x+1)). - Colin Barker, Dec 09 2012
EXAMPLE
The first five polynomials p(n,x) and their reductions are as follows:
p(0,x)=1 -> 1
p(1,x)=2x -> 2x
p(2,x)=4+x+3x^2 -> 7+4x
p(3,x)=16x+4x^2+4x^3 -> 16+20x
p(4,x)=16+8x+41x^2+10x^3+5x^4 -> 73+68x.
From these, read
A192376=(1,0,7,16,73,...) and A192377=(0,2,4,20,68,...)
MATHEMATICA
See A192376.
CROSSREFS
Sequence in context: A274520 A337616 A238229 * A286344 A279153 A204550
KEYWORD
nonn,easy
AUTHOR
Clark Kimberling, Jun 29 2011
STATUS
approved