A010687 -id:A010687 - cp's OEIS frontend

A040011 Continued fraction for sqrt(15).

3, 1, 6, 1, 6, 1, 6, 1, 6, 1, 6, 1, 6, 1, 6, 1, 6, 1, 6, 1, 6, 1, 6, 1, 6, 1, 6, 1, 6, 1, 6, 1, 6, 1, 6, 1, 6, 1, 6, 1, 6, 1, 6, 1, 6, 1, 6, 1, 6, 1, 6, 1, 6, 1, 6, 1, 6, 1, 6, 1, 6, 1, 6, 1, 6, 1, 6, 1, 6, 1, 6, 1, 6, 1, 6, 1, 6, 1, 6, 1, 6

Offset: 0

N. J. A. Sloane

Decimal expansion of 313/990. - R. J. Mathar, Aug 22 2025

			3.872983346207416885179265399... = 3 + 1/(1 + 1/(6 + 1/(1 + 1/(6 + ...)))). - _Harry J. Smith_, Jun 03 2009

James J. Tattersall, Elementary Number Theory in Nine Chapters, Cambridge University Press, 1999, page 276.

Harry J. Smith, Table of n, a(n) for n = 0..20000
G. Xiao, Contfrac.
Index entries for continued fractions for constants.
Index entries for linear recurrences with constant coefficients, signature (0,1).

Cf. A010472 (decimal expansion). A010687.

Digits := 100: convert(evalf(sqrt(N)),confrac,90,'cvgts'):

ContinuedFraction[Sqrt[15],300] (* Vladimir Joseph Stephan Orlovsky, Mar 05 2011 *)
PadRight[{3},120,{6,1}] (* Harvey P. Dale, Apr 14 2020 *)

{ allocatemem(932245000); default(realprecision, 19000); x=contfrac(sqrt(15)); for (n=0, 20000, write("b040011.txt", n, " ", x[n+1])); } \\ Harry J. Smith, Jun 03 2009

From Amiram Eldar, Nov 12 2023: (Start)
Multiplicative with a(2^e) = 6, and a(p^e) = 1 for an odd prime p.
Dirichlet g.f.: zeta(s) * (1 + 5/2^s). (End)
G.f.: (3 + x + 3*x^2)/(1 - x^2). - Stefano Spezia, Jul 26 2025

A047335 Numbers that are congruent to {0, 6} mod 7.

Original entry on oeis.org

0, 6, 7, 13, 14, 20, 21, 27, 28, 34, 35, 41, 42, 48, 49, 55, 56, 62, 63, 69, 70, 76, 77, 83, 84, 90, 91, 97, 98, 104, 105, 111, 112, 118, 119, 125, 126, 132, 133, 139, 140, 146, 147, 153, 154, 160, 161, 167, 168

Offset: 1

N. J. A. Sloane

Hsien-Kuei Hwang, S Janson, TH Tsai, Exact and asymptotic solutions of the recurrence f(n) = f(floor(n/2)) + f(ceiling(n/2)) + g(n): theory and applications, Preprint, 2016; http://140.109.74.92/hk/wp-content/files/2016/12/aat-hhrr-1.pdf. Also Exact and Asymptotic Solutions of a Divide-and-Conquer Recurrence Dividing at Half: Theory and Applications, ACM Transactions on Algorithms, 13:4 (2017), #47; DOI: 10.1145/3127585

Index entries for linear recurrences with constant coefficients, signature (1, 1, -1).

Cf. A274406.

Select[Range[0,200],MemberQ[{0,6},Mod[#,7]]&]  (* Harvey P. Dale, Mar 16 2011 *)

From Bruno Berselli, Oct 06 2010: (Start)
G.f.: x^2*(6+x)/((1+x)*(1-x)^2).
a(n) - a(n-1) - a(n-2) + a(n-3) = 0 (n > 3).
a(n) = (14*n + 5*(-1)^n - 9)/4.
a(n) - a(n-2) = 7 (n > 2).
a(n) - a(n-1) = A010687(k) with n > 1 and k == n-1 (mod 2). (End)
a(n+1) = Sum_{k>=0} A030308(n,k)*b(k) with b(0)=6 and b(k) = 7*2^(k-1) = A005009(k-1) for k > 0. - Philippe Deléham, Oct 18 2011

A176016 Decimal expansion of (3+sqrt(15))/6.

Original entry on oeis.org

1, 1, 4, 5, 4, 9, 7, 2, 2, 4, 3, 6, 7, 9, 0, 2, 8, 1, 4, 1, 9, 6, 5, 4, 4, 2, 3, 3, 2, 9, 7, 0, 6, 6, 6, 0, 1, 8, 0, 5, 4, 8, 6, 9, 5, 0, 8, 8, 1, 9, 3, 1, 8, 0, 4, 4, 3, 1, 2, 6, 2, 2, 9, 4, 3, 5, 2, 2, 4, 7, 1, 8, 1, 9, 8, 9, 4, 9, 6, 5, 0, 5, 5, 8, 6, 5, 4, 7, 8, 9, 6, 1, 4, 3, 1, 1, 2, 2, 5, 2, 9, 8, 6, 0, 5

Offset: 1

Klaus Brockhaus, Apr 06 2010

Continued fraction expansion of (3+sqrt(15))/6 is A010687.

			(3+sqrt(15))/6 = 1.14549722436790281419...

Daniel Starodubtsev, Table of n, a(n) for n = 1..10000

Cf. A010472 (sqrt(15)), A176020 ((3+sqrt(15))/3), A010687 (repeat 1, 6).

RealDigits[(3+Sqrt[15])/6,10,120][[1]] (* Harvey P. Dale, May 01 2012 *)

Equals 1/2+A140246. - R. J. Mathar, Mar 17 2025

A146533 Catalan transform of A135092.

Original entry on oeis.org

1, 7, 21, 70, 245, 882, 3234, 12012, 45045, 170170, 646646, 2469012, 9464546, 36402100, 140408100, 542911320, 2103781365, 8167621770, 31762973550, 123708423300, 482462850870, 1883902560540, 7364346373020, 28817007546600, 112866612890850, 442437122532132, 1735714865318364

Offset: 0

Philippe Deléham, Oct 31 2008

nonn

Cf. A088218, A000984, A029651, A100320, A029609, A144706.

a[n_]:=(7*Binomial[2n,n]-5*KroneckerDelta[n,0])/2; Array[a,27,0] (* Stefano Spezia, Feb 14 2025 *)

a(n) = Sum_{k=0..n} A039599(n,k)*A010687(k) = Sum_{k=0..n} A106566(n,k)*A135092(k).
a(n) = (7*C(2n,n) - 5*0^n)/2.
From Stefano Spezia, Feb 14 2025: (Start)
G.f.: (7/sqrt(1 - 4*x) - 5)/2.
E.g.f.: (7*exp(2*x)*BesselI(0, 2*x) - 5)/2. (End)

a(23)-a(26) from Stefano Spezia, Feb 14 2025

A081193 a(n) = 6a(n-1)-8a(n-2) for n>1, a(0)=1, a(1)=9.

Original entry on oeis.org

1, 9, 46, 204, 856, 3504, 14176, 57024, 228736, 916224, 3667456, 14674944, 58710016, 234860544, 939483136, 3758014464, 15032221696, 60129214464, 240517513216, 962071363584, 3848288075776, 15393157545984, 61572640669696

Offset: 0

Paul Barry, Mar 11 2003

Third binomial transform of A010687 (period 2: repeat 1,6). [Bruno Berselli, Aug 06 2013]

Vincenzo Librandi, Table of n, a(n) for n = 0..200
Index entries for linear recurrences with constant coefficients, signature (6,-8).

[7*4^n/2-5*2^n/2: n in [0..25]]; // Vincenzo Librandi, Aug 07 2013

CoefficientList[Series[(1 + 3 x)/((1 - 2 x) (1 - 4 x)), {x, 0, 30}], x] (* Vincenzo Librandi, Aug 07 2013 *)

G.f.: (1+3*x)/((1-2*x)*(1-4*x)).

a(n) = 7*4^n/2-5*2^n/2.

A173261 Array T(n,k) read by antidiagonals: T(n,2k)=1, T(n,2k+1)=n, n>=2, k>=0.

Original entry on oeis.org

1, 1, 2, 1, 3, 1, 1, 4, 1, 2, 1, 5, 1, 3, 1, 1, 6, 1, 4, 1, 2, 1, 7, 1, 5, 1, 3, 1, 1, 8, 1, 6, 1, 4, 1, 2, 1, 9, 1, 7, 1, 5, 1, 3, 1, 1, 10, 1, 8, 1, 6, 1, 4, 1, 2, 1, 11, 1, 9, 1, 7, 1, 5, 1, 3, 1, 1, 12, 1, 10, 1, 8, 1, 6, 1, 4, 1, 2, 1, 13, 1, 11, 1, 9, 1, 7, 1, 5, 1, 3, 1, 1, 14, 1, 12, 1, 10, 1, 8, 1, 6, 1, 4, 1, 2

Offset: 2

Paul Curtz, Feb 14 2010

One may define another array B(n,0) = -1, B(n,k) = T(n,k-1) + 2*B(n,k-1), n>=2, which also starts in columns k>=0, as follows:
  -1, -1, 0, 1,  4,  9, 20,  41,  84, 169,  340,  681, 1364 ...: A084639;
  -1, -1, 1, 3,  9, 19, 41,  83, 169, 339,  681, 1363, 2729;
  -1, -1, 2, 5, 14, 29, 62, 125, 254, 509, 1022, 2045, 4094;
  -1, -1, 3, 7, 19, 39, 83, 167, 339, 679, 1363, 2727, 5459 ...: -A173114;
B(n,k) = (n-1)*A001045(k) - T(n,k).
First differences are B(n,k+1) - B(n,k) = (n-1)*A001045(k).

			The array T(n,k) starts in row n=2 with columns k>=0 as:
  1,  2, 1,  2, 1,  2, 1,  2, 1,  2, 1,  2 ... A000034;
  1,  3, 1,  3, 1,  3, 1,  3, 1,  3, 1,  3 ... A010684;
  1,  4, 1,  4, 1,  4, 1,  4, 1,  4, 1,  4 ... A010685;
  1,  5, 1,  5, 1,  5, 1,  5, 1,  5, 1,  5 ... A010686;
  1,  6, 1,  6, 1,  6, 1,  6, 1,  6, 1,  6 ... A010687;
  1,  7, 1,  7, 1,  7, 1,  7, 1,  7, 1,  7 ... A010688;
  1,  8, 1,  8, 1,  8, 1,  8, 1,  8, 1,  8 ... A010689;
  1,  9, 1,  9, 1,  9, 1,  9, 1,  9, 1,  9 ... A010690;
  1, 10, 1, 10, 1, 10, 1, 10, 1, 10, 1, 10 ... A010691.
Antidiagonal triangle begins as:
  1;
  1,  2;
  1,  3,  1;
  1,  4,  1,  2;
  1,  5,  1,  3,  1;
  1,  6,  1,  4,  1,  2;
  1,  7,  1,  5,  1,  3,  1;
  1,  8,  1,  6,  1,  4,  1,  2;
  1,  9,  1,  7,  1,  5,  1,  3,  1;
  1, 10,  1,  8,  1,  6,  1,  4,  1,  2;
  1, 11,  1,  9,  1,  7,  1,  5,  1,  3,  1;
  1, 12,  1, 10,  1,  8,  1,  6,  1,  4,  1,  2;
  1, 13,  1, 11,  1,  9,  1,  7,  1,  5,  1,  3,  1;
  1, 14,  1, 12,  1, 10,  1,  8,  1,  6,  1,  4,  1,  2;

G. C. Greubel, Antidiagonals n = 0..50 of the array, flattened

Cf. A000034, A010684, A010685, A010686, A010687, A010688, A010689, A010690, A010691.

Cf. A001045, A024206, A084639, A093178, A173114.

T[n_, k_]:= (1/2)*((n+3) - (n+1)*(-1)^k);
Table[T[n-k, k], {n,2,17}, {k,2,n}]//Flatten (* G. C. Greubel, Dec 03 2021 *)

flatten([[(1/2)*((n-k+3) - (n-k+1)*(-1)^k) for k in (2..n)] for n in (2..17)]) # G. C. Greubel, Dec 03 2021

From G. C. Greubel, Dec 03 2021: (Start)
T(n, k) = (1/2)*((n+3) - (n+1)*(-1)^k).
Sum_{k=0..n} T(n-k, k) = A024206(n).
Sum_{k=0..floor((n+2)/2)} T(n-2*k+2, k) = (1/16)*(2*n^2 4*n -5*(1 +(-1)^n) + 4*sin(n*Pi/2)) (diagonal sums).
T(2*n-2, n) = A093178(n). (End)

A176355 Periodic sequence: Repeat 6, 1.

Original entry on oeis.org

6, 1, 6, 1, 6, 1, 6, 1, 6, 1, 6, 1, 6, 1, 6, 1, 6, 1, 6, 1, 6, 1, 6, 1, 6, 1, 6, 1, 6, 1, 6, 1, 6, 1, 6, 1, 6, 1, 6, 1, 6, 1, 6, 1, 6, 1, 6, 1, 6, 1, 6, 1, 6, 1, 6, 1, 6, 1, 6, 1, 6, 1, 6, 1, 6, 1, 6, 1, 6, 1, 6, 1, 6, 1, 6, 1, 6, 1, 6, 1, 6, 1, 6, 1, 6, 1, 6, 1, 6, 1, 6, 1, 6, 1, 6, 1, 6, 1, 6, 1, 6, 1, 6, 1, 6

Offset: 0

Klaus Brockhaus, Apr 15 2010

Interleaving of A010722 and A000012.
Also continued fraction expansion of 3+sqrt(15).
Also decimal expansion of 61/99.
Essentially first differences of A047335.
Binomial transform of 6 followed by A166577 without initial terms 1, 4.
Inverse binomial transform of A005009 preceded by 6.

			0.6161616161616161616161616161616161616161...

Index entries for linear recurrences with constant coefficients, signature (0,1).

Cf. A010722 (all 6's sequence), A000012 (all 1's sequence), A092294 (decimal expansion of 3+sqrt(15)), A010687 (repeat 1, 6), A047335 (congruent to 0 or 6 mod 7), A166577, A005009 (7*2^n).

Magma
```
&cat[ [6, 1]: n in [0..52] ];
```
Magma
```
[(7+5*(-1)^n)/2: n in [0..104]];
```

PadRight[{},120,{6,1}] (* Harvey P. Dale, Apr 12 2018 *)

G.f.: (6 + x)/(1 - x^2).
a(n) = (7 + 5*(-1)^n)/2.
a(n) = a(n-2) for n>1, a(0)=6, a(1)=1.
a(n) = -a(n-1)+7 for n>0, a(0)=6.
a(n) = 6*((n+1) mod 2) + (n mod 2).
a(n) = A010687(n+1).
a(n) = 13^n mod 7. - Vincenzo Librandi, Jun 01 2016
From Amiram Eldar, Jan 01 2023: (Start)
Multiplicative with a(2^e) = 6, and a(p^e) = 1 for p >= 3.
Dirichlet g.f.: zeta(s)*(1+5/2^s). (End)
E.g.f.: 6*cosh(x) + sinh(x). - Stefano Spezia, Feb 09 2025

cp's OEIS Frontend

A040011 Continued fraction for sqrt(15).

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A047335 Numbers that are congruent to {0, 6} mod 7.

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A176016 Decimal expansion of (3+sqrt(15))/6.

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A146533 Catalan transform of A135092.

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A081193 a(n) = 6*a(n-1)-8*a(n-2) for n>1, a(0)=1, a(1)=9.

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A173261 Array T(n,k) read by antidiagonals: T(n,2k)=1, T(n,2k+1)=n, n>=2, k>=0.

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A176355 Periodic sequence: Repeat 6, 1.

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A081193 a(n) = 6a(n-1)-8a(n-2) for n>1, a(0)=1, a(1)=9.