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A235348 Series reversion of x*(1-2*x-5*x^2)/(1-x^2). 1
1, 2, 12, 82, 636, 5266, 45684, 409706, 3768132, 35346082, 336854844, 3252391170, 31746462732, 312755404818, 3105750620772, 31054695744570, 312404601250644, 3159598296022978, 32108181705850860, 327682918265502002, 3357089384702757276 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Sum of turbulence series A107841 and A235347.

LINKS

Fung Lam, Table of n, a(n) for n = 1..1000

MATHEMATICA

Rest[CoefficientList[InverseSeries[Series[x*(1-2*x-5*x^2)/(1-x^2), {x, 0, 20}], x], x]] (* Vaclav Kotesovec, Jan 29 2014 *)

PROG

(Python)

# a235348. The list a has been calculated (len(a)>=3)

m = len(a)

if m%2 ==0:

....b = (a[m/2-1])**2

else:

....b = 0

d = 0

for i in range (1, m+3):

....for j in range (1, m+3):

........if (i+j)%m ==0 and (i+j) <= m and i!=j:

............d = d + a[i-1]*a[j-1]

f = 0

for i in range (1, m+1):

....for j in range (1, m+1):

........if (i+j)%(m+1) ==0 and (i+j) <= (m+1):

............f = f + a[i-1]*a[j-1]

g = 0

for i in range (1, m+1):

....for j in range (1, m+1):

........for k in range (1, m+1):

............if (i+j+k)%(m+1) ==0 and (i+j+k) <= (m+1):

g = g + a[i-1]*a[j-1]*a[k-1]

y = 5*g + 2*f - b - d

# a235348.

(PARI) Vec( serreverse(x*(1-2*x-5*x^2)/(1-x^2) +O(x^66) ) ) \\ Joerg Arndt, Jan 14 2014

CROSSREFS

Sequence in context: A055548 A092850 A199420 * A052864 A136278 A130464

Adjacent sequences:  A235345 A235346 A235347 * A235349 A235350 A235351

KEYWORD

nonn,easy

AUTHOR

Fung Lam, Jan 13 2014

STATUS

approved

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Last modified January 22 10:13 EST 2022. Contains 350481 sequences. (Running on oeis4.)