cp's OEIS Frontend

This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.

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A256045 Triangle read by rows: order of all-2s configuration on the n X k sandpile grid graph.

Original entry on oeis.org

2, 3, 1, 7, 7, 8, 11, 5, 71, 3, 26, 9, 679, 77, 52, 41, 13, 769, 281, 17753, 29, 97, 47, 3713, 4271, 726433, 434657, 272, 153, 17, 8449, 2245, 33507, 167089, 46069729, 901, 362, 123, 81767, 8569, 24852386, 265721, 8118481057, 190818387, 73124, 571, 89, 93127, 18061, 20721019, 4213133, 4974089647, 1031151241, 1234496016491, 89893
Offset: 1

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Author

N. J. A. Sloane, Mar 15 2015

Keywords

Examples

			Triangle begins:
[2]
[3, 1]
[7, 7, 8]
[11, 5, 71, 3]
[26, 9, 679, 77, 52]
[41, 13, 769, 281, 17753, 29]
[97, 47, 3713, 4271, 726433, 434657, 272]
[153, 17, 8449, 2245, 33507, 167089, 46069729, 901]
[362, 123, 81767, 8569, 24852386, 265721, 8118481057, 190818387, 73124]
[571, 89, 93127, 18061, 20721019, 4213133, 4974089647, 1031151241, 1234496016491, 89893]
...
		

Crossrefs

Main diagonal gives A256046, A256043, and A256047.

Formula

From Andrey Zabolotskiy, Oct 22 2021: (Start)
It seems that T(k, 1) = A005246(k+2).
For the formula for T(k, 2), see the last theorem of Morar and Perkinson in Perkinson's slides. In particular, T(2*k, 2) = A195549(k).
T(n, k) divides A348566(n, k). (End)

Extensions

Column 1 added by Andrey Zabolotskiy, Oct 22 2021

A076736 Let u(1) = u(2) = u(3) = 2, u(n) = (1 + u(n-1)*u(n-2))/u(n-3); then a(n) is the denominator of u(n).

Original entry on oeis.org

1, 1, 1, 2, 1, 4, 2, 8, 4, 16, 8, 32, 16, 64, 32, 128, 64, 256, 128, 512, 256, 1024, 512, 2048, 1024, 4096, 2048, 8192, 4096, 16384, 8192, 32768, 16384, 65536, 32768, 131072, 65536, 262144, 131072, 524288, 262144, 1048576, 524288, 2097152
Offset: 1

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Author

Benoit Cloitre, Nov 24 2002

Keywords

Comments

The sequence 1,4,2,8,4,... has g.f. (1+4*x)/(1-2*x^2) and a(n) = 2^(n/2)*(1+2*sqrt(2) + (1-2*sqrt(2))*(-1)^n)/2. - Paul Barry, Apr 26 2004
The sequence 2,1,4,2,8,... has a(n) = 2^(n/2)*(1+2*sqrt(2)-(1-2*sqrt(2))*(-1)^n)/(2*sqrt(2)) and is essentially the pair-reversal of A016116. - Paul Barry, Apr 26 2004

Crossrefs

Programs

  • Mathematica
    LinearRecurrence[{0,2},{1,1,1,2,1},50] (* Harvey P. Dale, Aug 25 2015 *)

Formula

For n > 4, a(n) = 2^A028242(n-4).
From Colin Barker, Oct 14 2014: (Start)
For n > 5, a(n) = 2*a(n-2).
G.f.: x*(x-1)*(x^3+x^2+2*x+1) / (2*x^2-1). (End)

Extensions

More terms from Paul Barry, Apr 26 2004

A208207 a(n)=(a(n-1)^3*a(n-2)+1)/a(n-3) with a(0)=a(1)=a(2)=1.

Original entry on oeis.org

1, 1, 1, 2, 9, 1459, 13975855106, 442535332406378982945622818194705
Offset: 0

Views

Author

Matthew C. Russell, Apr 23 2012

Keywords

Comments

This is the case a=1, b=3, y(0)=y(1)=y(2)=1 of the recurrence shown in the Example 3.2 of "The Laurent phenomenon" (see Link lines, p. 10).
The next term has 105 digits. - Harvey P. Dale, Jul 04 2022

Crossrefs

Programs

  • Maple
    a:=proc(n) if n<3 then return 1: fi: return (a(n-1)^3*a(n-2)+1)/a(n-3): end: seq(a(i),i=0..10);
  • Mathematica
    RecurrenceTable[{a[n] == (a[n - 1]^3*a[n - 2] + 1)/a[n - 3], a[0] == a[1] == a[2] == 1}, a, {n, 0, 8}] (* Michael De Vlieger, Mar 19 2017 *)
    nxt[{a_, b_, c_}] := {b, c, (c^3 b + 1)/a}; NestList[nxt,{1,1,1},10][[All,1]] (* Harvey P. Dale, Jul 04 2022 *)

Formula

From Vaclav Kotesovec, May 20 2015: (Start)
a(n) ~ c1^(d1^n) * c2^(d2^n) * c3^(d3^n), where
d1 = -0.675130870566646070889621798150060480808032527677372732612153869841...
d2 = 0.4608111271891108834741240973014799919001128904578732982807715533323...
d3 = 3.2143197433775351874154977008485804889079196372194994343313823165091...
are the roots of the equation d^3 + 1 = 3*d^2 + d and
c1 = 0.8399660110229591295951614867364338523629139731316529610703364786466...
c2 = 0.5166029105674572719002224224720428001985297645051505025129589573676...
c3 = 1.0214282112585594227681235564690028577352359049566082298453239674712...
(End)

A208210 a(n)=(a(n-1)^2*a(n-2)^3+1)/a(n-3) with a(0)=a(1)=a(2)=1.

Original entry on oeis.org

1, 1, 1, 2, 5, 201, 2525063, 10355298070412763074, 8589063344901709900442551790362661608528200120823830773
Offset: 0

Views

Author

Matthew C. Russell, Apr 23 2012

Keywords

Comments

This is the case a=3, b=2, y(0)=y(1)=y(2)=1 of the recurrence shown in the Example 3.2 of "The Laurent phenomenon" (see Link lines, p. 10).
The next term -- a(9) -- has 161 digits. - Harvey P. Dale, Apr 14 2022

Crossrefs

Programs

  • Maple
    a:=proc(n) if n<3 then return 1: fi: return (a(n-1)^2*a(n-2)^3+1)/a(n-3): end: seq(a(i),i=0..10);
  • Mathematica
    a[0] = a[1] = a[2] = 1; a[n_] := a[n] = (a[n-1]^2*a[n-2]^3 + 1)/a[n-3];
    Array[a, 10, 0] (* Jean-François Alcover, Dec 14 2017 *)
    nxt[{a_,b_,c_}]:={b,c,(c^2 b^3+1)/a}; NestList[nxt,{1,1,1},10][[All,1]] (* Harvey P. Dale, Apr 14 2022 *)

Formula

From Vaclav Kotesovec, May 20 2015: (Start)
a(n) ~ c1^(d1^n) * c2^(d2^n) * c3^(d3^n), where
d1 = -1.198691243515997113071999692569776193916276872472594369204332359716...
d2 = 0.2864620650316004980582127604312427653427138786836169481458128553091...
d3 = 2.9122291784843966150137869321385334285735629937889774210585195044073...
are the roots of the equation d^3 + 1 = 2*d^2 + 3*d and
c1 = 0.9326266928252752296152676800592959458631493222642463226349218269187...
c2 = 0.2535475214701961189033928082745089316567819534655391761010907360554...
c3 = 1.0248087086665041891835364490857429725941144848712661648932932629036...
(End)

A211956 Coefficients of a sequence of polynomials related to the Morgan-Voyce polynomials.

Original entry on oeis.org

1, 1, 1, 1, 1, 2, 1, 4, 2, 1, 6, 4, 1, 9, 12, 4, 1, 12, 20, 8, 1, 16, 40, 32, 8, 1, 20, 60, 56, 16, 1, 25, 100, 140, 80, 16, 1, 30, 140, 224, 144, 32, 1, 36, 210, 448, 432, 192, 32, 1, 42, 280, 672, 720, 352, 64, 1, 49, 392, 1176, 1680, 1232, 448, 64
Offset: 0

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Author

Peter Bala, Apr 30 2012

Keywords

Comments

The row generating polynomials R(n,x) of A211955 factorize in the ring Z[x] as R(n,x) = P(n,x)*P(n+1,x) for n >= 1: explicitly, P(2*n,x) = 1/2*(b(2*n,2*x) + 1)/b(n,2*x) and P(2*n+1,x) = b(n,2*x), where b(n,x) := Sum_{k = 0..n} binomial(n+k,2*k)*x^k are the Morgan-Voyce polynomials of A085478. This triangle lists the coefficients in ascending powers of x of the polynomials P(n,x).
The odd numbered rows of the present triangle produce triangle A123519; the even numbered row entries are recorded separately in A211957 and appear to equal the unsigned and row reversed form of A204021. The even numbered rows with a factor of 2^(k-1) removed from the k-th column entries produce triangle A208513.

Examples

			Triangle begins
.n\k.|..0....1....2....3....4
= = = = = = = = = = = = = = =
..0..|..1
..1..|..1
..2..|..1....1
..3..|..1....2
..4..|..1....4....2
..5..|..1....6....4
..6..|..1....9...12....4
..7..|..1...12...20....8
..8..|..1...16...40...32....8
..9..|..1...20...60...56...16
...
		

Crossrefs

Formula

T(n,0) = 1; for k > 0, T(2*n,k) = 2^k * binomial(n+k,2*k) = A123519(n,k);
for k > 0, T(2*n-1,k) = n/(n+k)*(2^k)*binomial(n+k,2*k) = 2^(k-1)*A208513(n,k).
O.g.f.: ((1+t)*(1-t^2)-t^2*x)/((1-t^2)^2-2*t^2*x) = 1 + t + (1+x)*t^2 + (1+2*x)*t^3 + (1+4*x+2*x^2)*t^4 + ....
Row generating polynomials: P(2*n,x) := 1/2*(b(2*n,2*x)+1)/b(n,2*x) and P(2*n+1,x) := b(n,2*x), where b(n,x) := Sum_{k = 0..n} binomial(n+k,2*k)*x^k are the Morgan-Voyce polynomials of A085478.
The product P(n,x)*P(n+1,x) is the n-th row polynomial of A211955.
In terms of T(n,x), the Chebyshev polynomials of the first kind, we have P(2*n,x) = T(2*n,u) and P(2*n+1,x) = 1/u*T(2*n+1,u), where u = sqrt((x+2)/2).
Other representations for the row polynomials include
P(2*n,x) = 1/2*(1+x+sqrt(x^2+2*x))^n + 1/2*(1+x-sqrt(x^2+2*x))^n;
P(2*n,x) = n*Sum_{k = 0..n}(-1)^(n-k)/(n+k) * binomial(n+k,2*k) * (2*x+4)^k for n >= 1;
P(2*n+1,x) = (2*n+1)*Sum_{k=0..n} (-1)^(n-k)/(n+k+1) * binomial(n+k+1,2*k+1) * (2*x+4)^k.
Recurrence equation: P(n+1,x)*P(n-2,x) - P(n,x)*P(n-1,x) = x.
Row sums A005246(n+2).

A143643 Numerators of the lower principal convergents and the lower intermediate convergents to 3^(1/2).

Original entry on oeis.org

1, 3, 5, 12, 19, 45, 71, 168, 265, 627, 989, 2340, 3691, 8733, 13775, 32592, 51409, 121635, 191861, 453948, 716035, 1694157, 2672279, 6322680, 9973081, 23596563, 37220045, 88063572, 138907099, 328657725, 518408351, 1226567328, 1934726305, 4577611587, 7220496869, 17083879020, 26947261171, 63757904493, 100568547815
Offset: 1

Views

Author

Clark Kimberling, Aug 27 2008

Keywords

Comments

The lower principal and intermediate convergents to 3^(1/2), beginning with 1/1, 3/2, 5/3, 12/7, 19/11, form a strictly increasing sequence; with essentially, numerators being this sequence and denominators being A005246.
sqrt(floor(a(n)^2/3)+1) = A005246(n+1). Also see A082630. - Richard R. Forberg, Nov 14 2013
a(n) = U_n(sqrt(6),1) for n odd and a(n) = 3*U_n(sqrt(6),1) for n even, where U_n(sqrt(R),Q) denotes the Lehmer sequence with parameters R and Q. This sequence is a strong divisibility sequence, that is, gcd(a(n),a(m)) = a(gcd(n,m)) for all positive integers n and m. Consequently, this sequence is a divisibility sequence: if n divides m then a(n) divides a(m). - Peter Bala, Sep 03 2019

Examples

			From _Peter Bala_, Sep 03 2019: (Start)
If p(n)/q(n) denotes the n-th convergent to the simple continued fraction alpha = [c(0); c(1), c(2), ...] then a lower semiconvergent is a rational number of the form ( p(2*n) + m*p(2*n+1) )/( q(2*n) + m*q(2*n+1) ) where 0 <= m <= c(2*n+2). The lower semiconvergents include the even-indexed convergents p(2*n)/q(2*n) and give an increasing sequence of approximations to alpha from below.
In this case the simple continued fraction expansion sqrt(3) = [1; 1, 2, 1, 2, ...] produces the sequence of convergents (p(n)/q(n))n>=0 = [1/1, 2/1, 5/3, 7/4, 19/11, 26,15, 71/41, ...].
Thus the increasing sequence of lower semiconvergents begins 1/1, (1 + 2)/(1 + 1) = 3/2, (1 + 2*2)/(1 + 2*1) = 5/3, (5 + 7)/(3 + 4) = 12/7, (5 + 2*7)/(3 + 2*4) = 19/11, ... with numerators 1, 3, 5, 12, 19, .... (End)
		

References

  • Serge Lang, Introduction to Diophantine Approximations, Addison-Wesley, New York, 1966.
  • Clark Kimberling, "Best lower and upper approximates to irrational numbers," Elemente der Mathematik, 52 (1997) 122-126.

Crossrefs

Formula

a(n) = 4*a(n-2)-a(n-4). G.f.: x*(1+3*x+x^2)/(1-4*x^2+x^4). - Colin Barker, Apr 28 2012

A208202 a(n) = (a(n-1)*a(n-2)^2+1)/a(n-3) with a(0)=a(1)=a(2)=1.

Original entry on oeis.org

1, 1, 1, 2, 3, 13, 59, 3324, 890065, 166683166499, 39725939269090918399, 1240040687243304530118746458657221560, 11740660815927242416329935330676365456512664243108711550072429939
Offset: 0

Views

Author

Matthew C. Russell, Apr 23 2012

Keywords

Comments

This is the case a=2, b=1, y(0)=y(1)=y(2)=1 of the recurrence shown in the Example 3.2 of "The Laurent phenomenon" (see Link lines, p. 10).

Crossrefs

Programs

  • Magma
    [n le 3 select 1 else (Self(n-1)*Self(n-2)^2+1)/Self(n-3): n in [1..13]]; // Bruno Berselli, Apr 24 2012
  • Mathematica
    RecurrenceTable[{a[0] == a[1] == a[2] == 1, a[n] == (a[n - 1] a[n - 2]^2 + 1)/a[n - 3]}, a, {n, 12}] (* Bruno Berselli, Apr 25 2012 *)
    (* The numerical values of the constants d1, d2, d3 *) Print[N[{Root[1-2*#1-#1^2+#1^3&,1], Root[1-2*#1-#1^2+#1^3&,2], Root[1-2*#1-#1^2+#1^3&,3]}, 80]]; (* and the constants c1, c2, c3 *) A208202 = RecurrenceTable[{a[0]==a[1]==a[2]==N[1,100], a[n] == (a[n-1]*a[n-2]^2 + 1)/a[n-3]}, a, {n,1,30}]; Table[Flatten[N[{Exp[cc1], Exp[cc2], Exp[cc3]}/.Solve[Table[Log[A208202[[n]]] == cc1*Root[1 - 2*#1 - #1^2 + #1^3&, 1]^n + cc2*Root[1 - 2*#1 - #1^2 + #1^3&, 2]^n + cc3*Root[1 - 2*#1 - #1^2 + #1^3&, 3]^n, {n, k, k+2}]],80]], {k, Length[A208202]-3, Length[A208202]-2}] (* Vaclav Kotesovec, May 20 2015 *)

Formula

From Vaclav Kotesovec, May 20 2015: (Start)
a(n) ~ c1^(d1^n) * c2^(d2^n) * c3^(d3^n), where
d1 = -1.24697960371746706105000976800847962126454946179280421073109887819...
d2 = 0.445041867912628808577805128993589518932711137529089910623974031794...
d3 = 1.801937735804838252472204639014890102331838324263714300107124846398...
are the roots of the equation d^3 + 1 = d^2 + 2*d and
c1 = 0.937508205283971584227188160392119895660526011507051773879367647962...
c2 = 0.127128212809518009874462927372545164747593272064601714573478901156...
c3 = 1.135040592200579625529345655593495454581148721169010026906480955795...
(End)

A208203 a(n) = (a(n-1)*a(n-2)^3+1)/a(n-3) with a(0)=a(1)=a(2)=1.

Original entry on oeis.org

1, 1, 1, 2, 3, 25, 338, 1760417, 2719102918193, 43888992061611808973481301345, 501206842313618355048837897498360450999462416742984495192498
Offset: 0

Views

Author

Matthew C. Russell, Apr 23 2012

Keywords

Comments

This is the case a=3, b=1, y(0)=y(1)=y(2)=1 of the recurrence shown in the Example 3.2 of "The Laurent phenomenon" (see Link lines, p. 10).

Crossrefs

Programs

  • Maple
    a:=proc(n) if n<3 then return 1: fi: return (a(n-1)*a(n-2)^3+1)/a(n-3): end: seq(a(i),i=0..10);
  • Mathematica
    a[0] = a[1] = a[2] = 1; a[n_] := a[n] = (a[n - 1]*a[n - 2]^3 + 1)/a[n - 3];
    Table[a[n], {n, 0, 13}] (* Jean-François Alcover, Dec 14 2017 *)
    nxt[{a_,b_,c_}]:={b,c,(c*b^3+1)/a}; NestList[nxt,{1,1,1},10][[;;,1]] (* Harvey P. Dale, Nov 19 2023 *)

Formula

From Vaclav Kotesovec, May 20 2015: (Start)
a(n) ~ c1^(d1^n) * c2^(d2^n) * c3^(d3^n), where
d1 = -1.481194304092015622633537241216857180552745216998476728395893140813...
d2 = 0.3111078174659818999302814767914862551326055871751667747271657344269...
d3 = 2.1700864866260337227032557644253709254201396298233099536687274063868...
are the roots of the equation d^3 + 1 = d^2 + 3*d and
c1 = 0.9558632550121524723294926402589664329208850973886195977958538648966...
c2 = 0.0925177857987965285678801091508493414479538300221910521000975614673...
c3 = 1.0621981744880569938247885786471114069804924018378928906529142898259...
(End)

A208204 a(n) = (a(n-1)*a(n-2)^4+1)/a(n-3) with a(0)=a(1)=a(2)=1.

Original entry on oeis.org

1, 1, 1, 2, 3, 49, 1985, 3814376662, 1208563686390770296199, 128885284912846137074628029815898112630258374651779168689
Offset: 0

Views

Author

Matthew C. Russell, Apr 23 2012

Keywords

Comments

This is the case a=4, b=1, y(0)=y(1)=y(2)=1 of the recurrence shown in the Example 3.2 of "The Laurent phenomenon" (see Link lines, p. 10).

Crossrefs

Programs

  • Maple
    a:=proc(n) if n<3 then return 1: fi: return (a(n-1)*a(n-2)^4+1)/a(n-3): end: seq(a(i),i=1..10);
  • Mathematica
    a[0] = a[1] = a[2] = 1; a[n_] := a[n] = (a[n - 1]*a[n - 2]^4 + 1)/a[n - 3];
    Table[a[n], {n, 0, 12}] (* Jean-François Alcover, Dec 14 2017 *)

Formula

From Vaclav Kotesovec, May 20 2015: (Start)
a(n) ~ c1^(d1^n) * c2^(d2^n) * c3^(d3^n), where
d1 = -1.699628148275317956229728291667145232598924547592878096541472700997...
d2 = 0.2391232782565544642500835033134825869161430421361867747730632704531...
d3 = 2.4605048700187634919796447883536626456827815054566913217684094305444...
are the roots of the equation d^3 + 1 = d^2 + 4*d and
c1 = 0.9668824482256124500532459849115781952211866063916062435395239896336...
c2 = 0.0680423294122660088493946488133224274885942757072304155092839505634...
c3 = 1.0386083844527725102069795872299989830277012965629707721463998933768...
(End)

A208211 a(n)=(a(n-1)^2*a(n-2)^4+1)/a(n-3) with a(0)=a(1)=a(2)=1.

Original entry on oeis.org

1, 1, 1, 2, 5, 401, 50250313, 13058251494934169005517674, 2711319949800838662068317571116321157238013748056632969662193456875554487084437
Offset: 0

Views

Author

Matthew C. Russell, Apr 23 2012

Keywords

Comments

This is the case a=4, b=2, y(0)=y(1)=y(2)=1 of the recurrence shown in the Example 3.2 of "The Laurent phenomenon" (see Link lines, p. 10).
The next term, a(9), has 250 digits. - Harvey P. Dale, May 12 2015

Crossrefs

Programs

  • Maple
    a:=proc(n) if n<3 then return 1: fi: return (a(n-1)^2*a(n-2)^4+1)/a(n-3): end: seq(a(i),i=0..10);
  • Mathematica
    RecurrenceTable[{a[0]==a[1]==a[2]==1,a[n]==(a[n-1]^2*a[n-2]^4+1)/a[n-3]},a,{n,9}] (* Harvey P. Dale, May 12 2015 *)

Formula

From Vaclav Kotesovec, May 20 2015: (Start)
a(n) ~ c1^(d1^n) * c2^(d2^n) * c3^(d3^n), where
d1 = -1.391382380630900845100729034616031832171938259539254240563846155543...
d2 = 0.2271344421706896320468868758105588761186297860618178147525916240716...
d3 = 3.1642479384602112130538421588054729560533084734774364258112545314714...
are the roots of the equation d^3 + 1 = 2*d^2 + 4*d and
c1 = 0.9492747639156309053009206968548726546571223067568220073025225799006...
c2 = 0.2025736158012536053359109009272747757676200151893348144191432397054...
c3 = 1.0182066570849459786725527422494583474915007718333213073686225606760...
(End)
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