A103625 a(n) = 3 + 7*a(n-2) + sqrt(1 + 48*a(n-2) + 48*a(n-2)^2), with a(1) = 0, a(2) = 0, a(3) = 2.
0, 0, 2, 4, 34, 62, 480, 870, 6692, 12124, 93214, 168872, 1298310, 2352090, 18083132, 32760394, 251865544, 456293432, 3508034490, 6355347660, 48860617322, 88518573814, 680540608024, 1232904685742, 9478707895020, 17172147026580, 132021369922262, 239177153686384
Offset: 1
Links
- G. C. Greubel, Table of n, a(n) for n = 1..1000
- Index entries for linear recurrences with constant coefficients, signature (1,14,-14,-1,1).
Programs
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Magma
R
:=PowerSeriesRing(Integers(), 30); [0,0] cat Coefficients(R!(2*(x^2+x+1)/(1-x-14*x^2+14*x^3+x^4-x^5))); // G. C. Greubel, Jul 15 2018 -
Mathematica
a[1]=0; a[2]=0; a[3]=2; a[n_]:=a[n]= 3+7a[n-2]+Sqrt[1+48a[n-2]+48a[n-2]^2]; Table[a[n],{n,1,20}] (* Herbert Kociemba, May 12 2008 *) Rest@CoefficientList[Series[2*x^3*(1+x+x^2)/(1-x-14*x^2+14*x^3+x^4-x^5), {x,0,30}], x] (* G. C. Greubel, Jul 15 2018 *) LinearRecurrence[{1,14,-14,-1,1},{0,0,2,4,34},30] (* Harvey P. Dale, Jun 04 2021 *) -
PARI
my(x='x+O('x^30)); concat([0,0], Vec(2*x^3*(1+x+x^2)/(1-x-14*x^2+14*x^3 + x^4-x^5))) \\ G. C. Greubel, Jul 15 2018 -
SageMath
@CachedFunction def b(n): return chebyshev_U(n, -2) # A125905 def A103625(n): return (1/8)*(-16*int(n==0) -4 +5*(-1)^n*(3*b(n) +11*b(n-1)) +5*b(n) +19*b(n-1)) [A103625(n) for n in range(1,41)] # G. C. Greubel, Mar 22 2024
Formula
G.f.: 2*x^3*(1+x+x^2)/((1-x)*(1-4*x+x^2)*(1+4*x+x^2)). - Ralf Stephan, May 18 2007
a(n) = (1/8)*(-16*[n=0] - 4 + 5*(-1)^n*(3*A125905(n) + 11*A125905(n-1)) + (5*A125905(n) + 19*A125905(n-1))), where A125905(n) = ChebyshevU(n, -2). - G. C. Greubel, Mar 22 2024
E.g.f.: (15*cosh(sqrt(3)*x)*(2*cosh(2*x) + sinh(2*x))/2 - sqrt(3)*(4*cosh(x) + sinh(x))*(cosh(x) + 4*sinh(x))*sinh(sqrt(3)*x) - 3*(4 + exp(x)))/6. - Stefano Spezia, Jun 02 2024
Extensions
Terms a(17) onward added by G. C. Greubel, Jul 15 2018
Edited by G. C. Greubel, Mar 22 2024
Comments