A026636 -id:A026636 - cp's OEIS frontend

A026961 Self-convolution of array T given by A026626.

1, 2, 11, 34, 138, 492, 1830, 6804, 25576, 96728, 367932, 1405884, 5392590, 20751504, 80076872, 309748096, 1200669828, 4662772672, 18137643524, 70657441212, 275620281310, 1076429623256, 4208562777342, 16470788108008, 64519534566362, 252948764993472, 992453764928050

Offset: 0

Clark Kimberling

nonn

G. C. Greubel, Table of n, a(n) for n = 0..1000

Cf. A026626, A026627, A026628, A026629, A026630, A026631, A026632.
Cf. A026633, A026634, A026635, A026636, A026962, A026963, A026964.
Cf. A026965.

p1:= func< n | -1864800 + 1239076*n + 7915984*n^2 - 11263411*n^3 + 5406551*n^4 - 1042185*n^5 + 65025*n^6 >;
p2:= func< n | -4505760 + 7236856*n + 10545958*n^2 - 20700889*n^3 + 10823147*n^4 - 2188767*n^5 + 143055*n^6 >;
p3:= func< n | -1522080 + 2667320*n + 3116288*n^2 - 6715322*n^3 + 3619972*n^4 - 755718*n^5 + 52020*n^6 >;
p4:= func< n | 42*(-376320 + 434044*n + 1225808*n^2 - 1997637*n^3 + 1002947*n^4 - 199767*n^5 + 13005*n^6) >;
p5:= func< n | 2*(-559440 + 1665230*n - 243157*n^2 - 1361078*n^3 + 898312*n^4 - 195432*n^5 + 13005*n^6) >;
I:=[11, 34, 138]; [1,2] cat [n le 3 select I[n] else (p1(n)*Self(n-1) + p2(n)*Self(n-2) + p3(n)*Self(n-3) + p4(n))/p5(n) : n in [1..40]]; // G. C. Greubel, Jun 21 2024

T[n_, k_]:= T[n, k]= If[k==0 || k==n, 1, If[k==1 || k==n-1, (6*n-1 + (-1)^n)/4, T[n-1,k-1] +T[n-1,k]]];
A026961[n_]:= A026961[n] = Sum[T[n,k]*T[n,n-k], {k,0,n}];
Table[A026961[n], {n,0,50}] (* G. C. Greubel, Jun 21 2024 *)

@CachedFunction
def T(n, k): # T = A026626
    if (k==0 or k==n): return 1
    elif (k==1 or k==n-1): return int(3*n//2)
    else: return T(n-1, k-1) + T(n-1, k)
def A026961(n): return sum(T(n,k)*T(n,n-k) for k in range(n+1))
[A026961(n) for n in range(41)] # G. C. Greubel, Jun 21 2024

From G. C. Greubel, Jun 21 2024: (Start)
a(n) = Sum_{k=0..n} T(n, k)*T(n, n-k). - G. C. Greubel, Jun 21 2024
a(n) = (p1(n)*a(n-1) + p2(n)*a(n-2) + p3(n)*a(n-3) + p4(n))/p5(n), where
  p1(n) = 22589280 - 75610404*n + 85542748*n^2 - 44611965*n^3 + 11592851*n^4 - 1432335*n^5 + 65025*n^6.
  p2(n) = 32659200 - 131052480*n + 161621002*n^2 - 88742247*n^3 + 23912807*n^4 - 3047097*n^5 + 143055*n^6.
  p3(n) = 2*(5034960 - 21140910*n + 26659783*n^2 - 14896395*n^3 + 4089431*n^4 - 533919*n^5 + 26010*n^6).
  p4(n) = 42*(3628800 - 13099136*n + 15429146*n^2 - 8267195*n^3 + 2196857*n^4 - 277797*n^5 + 13005*n^6).
  p5(n) = 2*n*(-6580128 + 11379344*n - 7168746*n^2 + 2070547*n^3 - 273462*n^4 + 13005*n^5). (End)

More terms from Sean A. Irvine, Oct 20 2019

A026962 a(n) = Sum_{k=0..n-1} T(n,k) * T(n,k+1), with T given by A026626.

Original entry on oeis.org

1, 6, 24, 108, 406, 1572, 5961, 22788, 87209, 335010, 1290376, 4983162, 19286891, 74797176, 290586771, 1130716508, 4406049037, 17191077082, 67152699384, 262594530318, 1027851765350, 4026831276662, 15788979175102, 61954847930374, 243278117470476, 955907159445522

Offset: 1

Clark Kimberling

nonn

G. C. Greubel, Table of n, a(n) for n = 1..1000

Cf. A026626, A026627, A026628, A026629, A026630, A026631, A026632.
Cf. A026633, A026634, A026635, A026636, A026961, A026963, A026964.
Cf. A026965.

T[n_, k_]:= T[n, k]= If[k==0 || k==n, 1, If[k==1 || k==n-1, Floor[3*n/2], T[n-1,k-1] +T[n-1,k]]]; (* T = A026626 *)
A262962[n_]:=Sum[T[n,k]*T[n,k+1], {k,0,n-1}];
Table[A262962[n], {n,40}] (* G. C. Greubel, Jun 23 2024 *)

@CachedFunction
def T(n, k): # T = A026626
    if (k==0 or k==n): return 1
    elif (k==1 or k==n-1): return int(3*n//2)
    else: return T(n-1, k-1) + T(n-1, k)
def A262962(n): return sum( T(n,k)*T(n,k+1) for k in range(n))
[A262962(n) for n in range(1,41)] # G. C. Greubel, Jun 23 2024

More terms from Sean A. Irvine, Oct 20 2019

A026963 a(n) = Sum_{k=0..n-2} T(n,k) * T(n,k+2), with T given by A026626.

Original entry on oeis.org

1, 8, 52, 224, 987, 3980, 16057, 63732, 252424, 996332, 3927977, 15471622, 60915547, 239794516, 943946193, 3716205884, 14632901696, 57631689776, 227042423404, 894698122022, 3526753844436, 13906101471344, 54848887043366, 216402159510134, 854053133294062, 3371593602442500

Offset: 2

Clark Kimberling

nonn

G. C. Greubel, Table of n, a(n) for n = 2..1000

Cf. A026626, A026627, A026628, A026629, A026630, A026631, A026632.
Cf. A026633, A026634, A026635, A026636, A026961, A026962, A026964.
Cf. A026965.

T[n_, k_]:= T[n, k]= If[k==0 || k==n, 1, If[k==1 || k==n-1, Floor[3*n/2], T[n-1,k-1] +T[n-1,k]]]; (* T = A026626 *)
A262963[n_]:= Sum[T[n,k]*T[n,k+2], {k,0,n-2}];
Table[A262963[n], {n,2,40}] (* G. C. Greubel, Jun 23 2024 *)

@CachedFunction
def T(n, k): # T = A026626
    if (k==0 or k==n): return 1
    elif (k==1 or k==n-1): return int(3*n//2)
    else: return T(n-1, k-1) + T(n-1, k)
def A262963(n): return sum( T(n,k)*T(n,k+2) for k in range(n-1))
[A262963(n) for n in range(2,41)] # G. C. Greubel, Jun 23 2024

More terms from Sean A. Irvine, Oct 20 2019

A026964 a(n) = Sum_{k=0..n-3} T(n,k) * T(n,k+3), with T given by A026626.

Original entry on oeis.org

1, 12, 77, 434, 1978, 8830, 37409, 156474, 644305, 2632506, 10684360, 43166246, 173768764, 697596990, 2794438513, 11174809302, 44626341136, 178018744896, 709505830530, 2825762505810, 11247704919634, 44749537493028, 177970696795672, 707580176408854, 2812524327414647

Offset: 3

Clark Kimberling

nonn

G. C. Greubel, Table of n, a(n) for n = 3..1000

Cf. A026626, A026627, A026628, A026629, A026630, A026631, A026632.
Cf. A026633, A026634, A026635, A026636, A026961, A026962, A026963.
Cf. A026965.

T[n_, k_]:= T[n, k]= If[k==0 || k==n, 1, If[k==1 || k==n-1, Floor[3*n/2], T[n-1,k-1] +T[n-1,k]]]; (* T = A026626 *)
A262964[n_]:= Sum[T[n,k]*T[n,k+3], {k,0,n-3}];
Table[A262964[n], {n,3,40}] (* G. C. Greubel, Jun 23 2024 *)

@CachedFunction
def T(n, k): # T = A026626
    if (k==0 or k==n): return 1
    elif (k==1 or k==n-1): return int(3*n//2)
    else: return T(n-1, k-1) + T(n-1, k)
def A262964(n): return sum( T(n,k)*T(n,k+3) for k in range(n-2))
[A262964(n) for n in range(3,41)] # G. C. Greubel, Jun 23 2024

More terms from Sean A. Irvine, Oct 20 2019

A026965 a(n) = Sum_{k=0..n} (k+1) * A026626(n,k).

Original entry on oeis.org

1, 3, 10, 25, 66, 154, 360, 810, 1810, 3982, 8700, 18850, 40614, 87030, 185680, 394570, 835578, 1763998, 3713700, 7798770, 16340302, 34166086, 71303160, 148548250, 308980386, 641728494, 1330992460, 2757055810, 5704253430

Offset: 0

Clark Kimberling

G. C. Greubel, Table of n, a(n) for n = 0..1000
Index entries for linear recurrences with constant coefficients, signature (4,-2,-8,7,4,-4).

Cf. A026626, A026627, A026628, A026629, A026630, A026631, A026632.
Cf. A026633, A026634, A026635, A026636, A026961, A026962, A026963.
Cf. A026964.

[n le 1 select 2*n+1 else (n+2)*(17*2^(n-2) -3 +(-1)^n)/6: n in [0..40]]; // G. C. Greubel, Jun 23 2024

Table[(n+2)*(17*2^(n-2) -3 +(-1)^n)/6 +(1/4)*(Boole[n==0] +3*Boole[n== 1]), {n,0,50}] (* G. C. Greubel, Jun 23 2024 *)

[(n+2)*(17*2^(n-2) -3 +(-1)^n)/6 + (1/4)*(int(n==0) + 3*int(n==1)) for n in range(41)] # G. C. Greubel, Jun 23 2024

G.f.: (1-x-x^3+3*x^4-5*x^5-2*x^6+3*x^7)/((1-x)^2*(1+x)^2*(1-2*x)^2). - Colin Barker, Apr 26 2015
From G. C. Greubel, Jun 23 2024: (Start)
a(n) = (1/6)*(n+2)*(17*2^(n-2) - 3 + (-1)^n) + (1/4)*([n=0] + 3*[n=1]).
a(n) = ( n*(n+2)*a(n-1) + 2*(n+1)*(n+2)*a(n-2) + n*(n+1)*(n+2) )/(n*(n + 1)), with a(0) = 1, a(1) = 3, a(2) = 10, a(3) = 25.
E.g.f.: (1/12)*( 17*(1+x)*exp(2*x) - 6*(2+x)*exp(x) + 2*(2-x)*exp(-x) + 3*(1+3*x) ). (End)

A080239 Antidiagonal sums of triangle A035317.

Original entry on oeis.org

1, 1, 2, 3, 6, 9, 15, 24, 40, 64, 104, 168, 273, 441, 714, 1155, 1870, 3025, 4895, 7920, 12816, 20736, 33552, 54288, 87841, 142129, 229970, 372099, 602070, 974169, 1576239, 2550408, 4126648, 6677056, 10803704, 17480760, 28284465, 45765225, 74049690

Offset: 1

Paul Barry, Feb 11 2003

Convolution of Fibonacci sequence with sequence (1, 0, 0, 0, 1, 0, 0, 0, 1, ...).
There is an interesting relation between a(n) and the Fibonacci sequence f(n). Sqrt(a(4n-2)) = f(2n). By using this fact we can calculate the value of a(n) by the following (1),(2),(3),(4) and (5). (1) a(1) = 1. (2) If n = 2 (mod 4), then a(n) = f((n+2)/2)^2. (3) If n = 3 (mod 4), then a(n) = (f((n+5)/2)^2-2f((n+1)/2)^2-1)/3. (4) If n = 0 (mod 4), then a(n) = (f((n+4)/2)^2+f(n/2)^2-1)/3. (5) If n = 1 (mod 4), then a(n) = (2f((n+3)/2)^2-f((n-1)/2)^2+1)/3. - Hiroshi Matsui and Ryohei Miyadera, Aug 08 2006
Sequences of the form s(0)=a, s(1)=b, s(n) = s(n-1) + s(n-2) + k if n mod m = p, else s(n) = s(n-1) + s(n-2) will have a form fib(n-1)*a + fib(n)*b + P(x)*k. a(n) is the P(x) sequence for m=4...s(n) = fib(n)*a + fib(n-1)*b + a(n-4-p)*k. - Gary Detlefs, Dec 05 2010
A different formula for a(n) as a function of the Fibonacci numbers f(n) may be conjectured. The pattern is of the form a(n) = f(p)*f(p-q) - 1 if n mod 4 = 3, else f(p)*f(p-q) where p = 2,2,4,4,4,4,6,6,6,6,8,8,8,8... and q = 0,1,3,2,0,1,3,2,0,1,3,2... p(n) = 2 * A002265(n+4) = 2*(floor((n+3)/2) - floor((n+3)/4)) (see comment by Jonathan Vos Post at A002265). A general formula for sequences having period 4 with terms a,b,c,d is given in A121262 (the discrete Fourier transform, as for all periodic sequences) and is a function of t(n)= 1/4*(2*cos(n*Pi/2) + 1 + (-1)^n). r4(a,b,c,d,n) = a*t(n+3) + b*t(n+2) + c*t(n+1) + d*t(n). This same formula may be used to subtract the 1 at n mod 4 = 3. a(n) = f(p(n))*f(p(n) - r4(1,0,3,2,n)) - r4(0,0,1,0,n). - Gary Detlefs, Dec 09 2010
This sequence is the sequence B4,1 on p. 34 of "Pascal-like triangles and Fibonacci-like sequences" in the references. In this article the authors treat more general sequences that have this sequence as an example. - Hiroshi Matsui and Ryohei Miyadera, Apr 11 2014
It is easy to see that a(n) = a(n-4) + f(n), where f(n) is the Fibonacci sequence. By using this repeatedly we have for a natural number m
a(4m) =a(4) + f(4m) + f(4m-4) + ... + f(8),
a(4m+1) = a(1) + f(4m) + f(4m-4) + ... + f(5),
a(4m+2) = a(2) + f(4m) + f(4m-4) + ... + f(6) and
a(4m+3) = a(3) + f(4m) + f(4m-4) + ... + f(7).
- Wataru Takeshita and Ryohei Miyadera, Apr 11 2014
a(n-1) counts partially ordered partitions of (n-1) into (1,2,3,4) where the position (order) of 2's is unimportant. E.g., a(5)=6 (n-1)=4 These are (4),(31),(13),(22),(211,121,112=one),(1111). - David Neil McGrath, May 12 2015

Reinhard Zumkeller, Table of n, a(n) for n = 1..1000
H. Matsui et al., Problem B-1019, Fibonacci Quarterly, Vol. 45, Number 2; 2007; p. 182.
H. Matsui and R. Miyadera et al., Pascal-like triangles and Fibonacci-like sequences, The Mathematical Gazette, Vol. 94, Number 529; March 2010; pp. 27-41.
Index entries for linear recurrences with constant coefficients, signature (1,1,0,1,-1,-1).

Cf. A000045, A004695, A026636, A026647, A035317.

List([1..40], n-> Sum([0..Int((n-1)/4)], k-> Fibonacci(n-4*k) )); # G. C. Greubel, Jul 13 2019

a080239 n = a080239_list !! (n-1)
a080239_list = 1 : 1 : zipWith (+)
   (tail a011765_list) (zipWith (+) a080239_list $ tail a080239_list)
-- Reinhard Zumkeller, Jan 06 2012

I:=[1,1,2,3,6,9]; [n le 6 select I[n] else Self(n-1)+Self(n-2)+Self(n-4)-Self(n-5)-Self(n-6): n in [1..50]]; // Vincenzo Librandi, Jun 07 2015

f:=proc(n) option remember; local t1; if n <= 2 then RETURN(1); fi: if n mod 4 = 1 then t1:=1 else t1:=0; fi: f(n-1)+f(n-2)+t1; end; [seq(f(n), n=1..100)]; # N. J. A. Sloane, May 25 2008
with(combinat): f:=n-> fibonacci(n): p:=n-> 2*(floor((n+3)/2)-floor((n+3)/4)): t:=n-> 1/4*(2*cos(n*Pi/2)+1+(-1)^n): r4:=(a,b,c,d,n)-> a*t(n+3)+b*t(n+2)+c*t(n+1)+d*t(n): seq(f(p(n))*f(p(n)-r4(1,0,3,2,n))-r4(0,0,1,0,n), n = 1..33); # Gary Detlefs, Dec 09 2010
with(combinat): a:=proc(n); add(fibonacci(n-4*k),k=0..floor((n-1)/4)) end: seq(a(n), n = 1..33); # Johannes W. Meijer, Apr 19 2012

(*f[n] is the Fibonacci sequence and a[n] is the sequence of A080239*) f[n_]:= f[n] =f[n-1] +f[n-2]; f[1]=1; f[2]=1; a[n_]:= Which[n==1, 1, Mod[n, 4]==2, f[(n+2)/2]^2, Mod[n, 4]==3, (f[(n+5)/2]^2 - 2f[(n + 1)/2]^2 -1)/3, Mod[n, 4]==0, (f[(n+4)/2]^2 + f[n/2]^2 -1)/3, Mod[n, 4] == 1, (2f[(n+3)/2]^2 -f[(n-1)/2]^2 +1)/3] (* Hiroshi Matsui and Ryohei Miyadera, Aug 08 2006 *)
a=0; b=0; lst={a,b}; Do[z=a+b+1; AppendTo[lst,z]; a=b; b=z; z=a+b; AppendTo[lst,z]; a=b; b=z; z=a+b; AppendTo[lst,z]; a=b; b=z; z=a+b; AppendTo[lst,z]; a=b; b=z,{n,4!}]; lst (* Vladimir Joseph Stephan Orlovsky, Feb 16 2010 *)
(* Let f[n] be the Fibonacci sequence and a2[n] the sequence A080239 expressed by another formula discovered by Wataru Takeshita and Ryohei Miyadera *)
f=Fibonacci; a2[n_]:= Block[{m, s}, s = Mod[n, 4]; m = (n-s)/4;
Which[n==1, 1, n==2, 1, n==3, 2, s==0, 3 + Sum[f[4 i], {i, 2, m}], s == 1, 1 + Sum[f[4i+1], {i, 1, m}], s==2, 1 + Sum[f[4i+2], {i, 1, m}], s == 3, 2 + Sum[f[4i+3], {i, 1, m}]]]; Table[a2[n], {n, 1, 40}] (* Ryohei Miyadera, Apr 11 2014, minor update by Jean-François Alcover, Apr 29 2014 *)
LinearRecurrence[{1, 1, 0, 1, -1, -1}, {1, 1, 2, 3, 6, 9}, 41] (* Vincenzo Librandi, Jun 07 2015 *)

vector(40, n, f=fibonacci; sum(k=0,((n-1)\4), f(n-4*k))) \\ G. C. Greubel, Jul 13 2019

[sum(fibonacci(n-4*k) for k in (0..floor((n-1)/4))) for n in (1..40)] # G. C. Greubel, Jul 13 2019

G.f.: x/((1-x^4)(1 - x - x^2)) = x/(1 - x - x^2 - x^4 + x^5 + x^6).
a(n) = a(n-1) + a(n-2) + a(n-4) - a(n-5) - a(n-6).
a(n) = Sum_{j=0..floor(n/2)} Sum_{k=0..floor((n-j)/2)} binomial(n-j-2k, j-2k) for n>=0.
Another recurrence is given in the Maple code.
If n mod 4 = 1 then a(n) = a(n-1) + a(n-2) + 1, else a(n)= a(n-1) + a(n-2). - Gary Detlefs, Dec 05 2010
a(4n) = A058038(n) = Fibonacci(2n+2)*Fibonacci(2n).
a(4n+1) = A081016(n) = Fibonacci(2n+2)*Fibonacci(2n+1).
a(4n+2) = A049682(n+1) = Fibonacci(2n+2)^2.
a(4n+3) = A081018(n+1) = Fibonacci(2n+2)*Fibonacci(2n+3).
a(n) = 8*a(n-4) - 8*a(n-8) + a(n-12), n>12. - Gary Detlefs, Dec 10 2010
a(n+1) = a(n) + a(n-1) + A011765(n+1). - Reinhard Zumkeller, Jan 06 2012
a(n) = Sum_{k=0..floor((n-1)/4)} Fibonacci(n-4*k). - Johannes W. Meijer, Apr 19 2012

cp's OEIS Frontend

A026961 Self-convolution of array T given by A026626.

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A026962 a(n) = Sum_{k=0..n-1} T(n,k) * T(n,k+1), with T given by A026626.

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A026963 a(n) = Sum_{k=0..n-2} T(n,k) * T(n,k+2), with T given by A026626.

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A026964 a(n) = Sum_{k=0..n-3} T(n,k) * T(n,k+3), with T given by A026626.

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A026965 a(n) = Sum_{k=0..n} (k+1) * A026626(n,k).

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A080239 Antidiagonal sums of triangle A035317.

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