A127975 -id:A127975 - cp's OEIS frontend

A111575 Powers of 3 repeated four times.

1, 1, 1, 1, 3, 3, 3, 3, 9, 9, 9, 9, 27, 27, 27, 27, 81, 81, 81, 81, 243, 243, 243, 243, 729, 729, 729, 729, 2187, 2187, 2187, 2187, 6561, 6561, 6561, 6561, 19683, 19683, 19683, 19683, 59049, 59049, 59049, 59049, 177147, 177147, 177147, 177147, 531441

Offset: 0

Jeremy Gardiner, Nov 17 2005

Generating sequence for the number of 0's and 1's (run lengths) in the parity of A006072, A111065 and A118594.

			a(10) = 3^floor(10/4) = 3^2 = 9.

Vincenzo Librandi, Table of n, a(n) for n = 0..8000
Index entries for linear recurrences with constant coefficients, signature (0, 0, 0, 3).

Cf. A006072, A111065, A108411, A118594, A127975.

[3^(Floor(n/4)):n in [0..50]]; // Vincenzo Librandi, Sep 20 2011

With[{pt=3^Range[0,15]},Sort[Join[pt,pt,pt,pt]]] (* Harvey P. Dale, Sep 17 2011 *)
Table[PadRight[{},4,3^n],{n,0,15}]//Flatten (* Harvey P. Dale, Jan 17 2019 *)

a(n)=3^(n\4) \\ Charles R Greathouse IV, Oct 03 2016

a(n) = 3^floor(n/4).

O.g.f.: -(1+x)*(1+x^2)/(-1+3*x^4). - R. J. Mathar, Jan 08 2008

A127974 Numerators in expansion of (1-x)^(-2/3).

Original entry on oeis.org

1, 2, 5, 40, 110, 308, 2618, 7480, 21505, 559130, 1621477, 4717024, 41273960, 120646960, 353323240, 3109244512, 9133405754, 26862958100, 711868389650, 2098138411600, 6189508314220, 54821359354520, 161972198092900

Offset: 0

Paul Barry, Feb 09 2007

Numerators of n!/A008544(n) are A127975.

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

Cf. A001790, A008544, A104133, A127975.

Numerator[CoefficientList[Series[(1 - x)^(-2/3), {x, 0, 50}], x]] (* G. C. Greubel, May 07 2018 *)

a(n) = denominator(n!/A008544(n)).
a(n) = denominator(n!/(Product_{k=0..n-1} (2+3*k))).
Conjecture: a(n-1) = the numerator of (1/(2*sqrt(3)*Pi)) * Integral_{x >= 0} 1/(1 + x^3)^n. - Peter Bala, Jun 11 2024

A371636 For any number k >= 0, let T_k be the triangle with values in {-1, 0, +1} whose base corresponds to the balanced ternary expansion of k (without leading zeros) and other values, say t above u and v, satisfy t+u+v = 0 mod 3; this sequence lists the numbers k such that T_k has 3-fold rotational symmetry.

Original entry on oeis.org

0, 1, 4, 13, 19, 25, 40, 103, 112, 121, 154, 214, 364, 442, 505, 595, 673, 763, 826, 913, 1003, 1093, 1144, 1369, 1621, 1915, 2167, 2392, 2776, 3028, 3280, 3628, 4420, 4996, 5668, 6244, 7036, 8203, 9022, 9841, 10459, 10594, 11782, 12304, 13411, 13627, 14419

Offset: 1

Rémy Sigrist, Mar 30 2024

This sequence is a variant of A334556 and A361818.
This sequence is infinite as it contains A003462.
Empirically, for any w > 0, there are A127975(w-1) terms with w balanced ternary digits (ignoring leading zeros).
If k is a term then A338246(k) is also a term.

			The balanced ternary expansion of 595 is "1T11001" (where T denotes -1), and the corresponding triangle T_595 is as follows:
           1
          T 0
         1 0 0
        1 1 T 1
       0 T 0 1 1
      0 0 1 T 0 T
     1 T 1 1 0 0 1
As this triangle has 3-fold rotational symmetry, 595 belongs to the sequence.

Rémy Sigrist, Triangles illustrating initial terms (blue, gray and red respectively denote -1's, 0's and 1's)
Rémy Sigrist, PARI program
Index entries for sequences related to XOR-triangles

Cf. A003462, A127975, A334556, A338246, A361818, A371635.

PARI
```
\\ See Links section.
```

A242763 a(n) = 1 for n <= 7; a(n) = a(n-5) + a(n-7) for n>7.

Original entry on oeis.org

1, 1, 1, 1, 1, 1, 1, 2, 2, 2, 2, 2, 3, 3, 4, 4, 4, 5, 5, 7, 7, 8, 9, 9, 12, 12, 15, 16, 17, 21, 21, 27, 28, 32, 37, 38, 48, 49, 59, 65, 70, 85, 87, 107, 114, 129, 150, 157, 192, 201, 236, 264, 286, 342, 358, 428, 465, 522, 606, 644, 770, 823, 950, 1071, 1166, 1376

Offset: 1

Vicente Jesús Maniega Granado, Oct 03 2016

Generalized Fibonacci growth sequence using i = 2 as maturity period, j = 5 as conception period, and k = 2 as growth factor.

Maturity period is the number of periods that a Fibonacci tree node needs for being able to start developing branches. Conception period is the number of periods in a Fibonacci tree node needed to develop new branches since its maturity. Growth factor is the number of additional branches developed by a Fibonacci tree node, plus 1, and equals the base of the exponential series related to the given tree if maturity factor would be zero. Standard Fibonacci would use 1 as maturity period, 1 as conception period, and 2 as growth factor as the series becomes equal to 2^n with a maturity period of 0. Related to Lucas sequences.

			For n = 13 the a(13) = a(8) + a(6) = 2 + 1 = 3.

Colin Barker, Table of n, a(n) for n = 1..1000
Julia Collins, Fibonacci Tree
Fractal Foundation, Fibonacci Fractals
D. H. Lehmer, An extended theory of Lucas' functions, Annals of Mathematics, Second Series, Vol. 31, No. 3 (Jul., 1930), pp. 419-448.
Index entries for linear recurrences with constant coefficients, signature (0,0,0,0,1,0,1).

Cf. A000079 (i = 0, j = 1, k = 2), A000244 (i = 0, j = 1, k = 3), A000302 (i = 0, j = 1, k = 4), A000351 (i = 0, j = 1, k = 5), A000400 (i = 0, j = 1, k = 6), A000420 (i = 0, j = 1, k = 7), A001018 (i = 0, j = 1, k = 8), A001019 (i = 0, j = 1, k = 9), A011557 (i = 0, j = 1, k = 10), A001020 (i = 0, j = 1, k = 11), A001021 (i = 0, j = 1, k = 12), A016116 (i = 0, j = 2, k = 2), A108411 (i = 0, j = 2, k = 3), A213173 (i = 0, j = 2, k = 4), A074872 (i = 0, j = 2, k = 5), A173862 (i = 0, j = 3, k = 2), A127975 (i = 0, j = 3, k = 3), A200675 (i = 0, j = 4, k = 2), A111575 (i = 0, j = 4, k = 3), A000045 (i = 1, j = 1, k = 2), A001045 (i = 1, j = 1, k = 3), A006130 (i = 1, j = 1, k = 4), A006131 (i = 1, j = 1, k = 5), A015440 (i = 1, j = 1, k = 6), A015441 (i = 1, j = 1, k = 7), A015442 (i = 1, j = 1, k = 8), A015443 (i = 1, j = 1, k = 9), A015445 (i = 1, j = 1, k = 10), A015446 (i = 1, j = 1, k = 11), A015447 (i = 1, j = 1, k = 12), A000931 (i = 1, j = 2, k = 2), A159284 (i = 1, j = 2, k = 3), A238389 (i = 1, j = 2, k = 4), A097041 (i = 1, j = 2, k = 10), A079398 (i = 1, j = 3, k = 2), A103372 (i = 1, j = 4, k = 2), A103373 (i = 1, j = 5, k = 2), A103374 (i = 1, j = 6, k = 2), A000930 (i = 2, j = 1, k = 2), A077949 (i = 2, j = 1, k = 3), A084386 (i = 2, j = 1, k = 4), A089977 (i = 2, j = 1, k = 5), A178205 (i = 2, j = 1, k = 11), A103609 (i = 2, j = 2, k = 2), A077953 (i = 2, j = 2, k = 3), A226503 (i = 2, j = 3, k = 2), A122521 (i = 2, j = 6, k = 2), A003269 (i = 3, j = 1, k = 2), A052942 (i = 3, j = 1, k = 3), A005686 (i = 3, j = 2, k = 2), A237714 (i = 3, j = 2, k = 3), A238391 (i = 3, j = 2, k = 4), A247049 (i = 3, j = 3, k = 2), A077886 (i = 3, j = 3, k = 3), A003520 (i = 4, j = 1, k = 2), A108104 (i = 4, j = 2, k = 2), A005708 (i = 5, j = 1, k = 2), A237716 (i = 5, j = 2, k = 3), A005709 (i = 6, j = 1, k = 2), A122522 (i = 6, j = 2, k = 2), A005710 (i = 7, j = 1, k = 2), A237718 (i = 7, j = 2, k = 3), A017903 (i = 8, j = 1, k = 2).

[n le 7 select 1 else Self(n-5)+Self(n-7): n in [1..70]]; // Vincenzo Librandi, Nov 30 2016

LinearRecurrence[{0, 0, 0, 0, 1, 0, 1}, {1, 1, 1, 1, 1, 1, 1}, 70] (*  or *)
CoefficientList[ Series[(1+x+x^2+x^3+x^4)/(1-x^5-x^7), {x, 0, 70}], x] (* Robert G. Wilson v, Nov 25 2016 *)
nxt[{a_,b_,c_,d_,e_,f_,g_}]:={b,c,d,e,f,g,a+c}; NestList[nxt,{1,1,1,1,1,1,1},70][[;;,1]] (* Harvey P. Dale, Oct 22 2024 *)

Vec(x*(1+x+x^2+x^3+x^4)/((1-x+x^2)*(1+x-x^3-x^4-x^5)) + O(x^100)) \\ Colin Barker, Oct 27 2016

@CachedFunction # a = A242763
def a(n): return 1 if n<8 else a(n-5) +a(n-7)
[a(n) for n in range(1,76)] # G. C. Greubel, Oct 23 2024

Generic a(n) = 1 for n <= i+j; a(n) = a(n-j) + (k-1)*a(n-(i+j)) for n>i+j where i = maturity period, j = conception period, k = growth factor.
G.f.: x*(1+x+x^2+x^3+x^4) / ((1-x+x^2)*(1+x-x^3-x^4-x^5)). - Colin Barker, Oct 09 2016
Generic g.f.: x*(Sum_{l=0..j-1} x^l) / (1-x^j-(k-1)*x^(i+j)), with i > 0, j > 0 and k > 1.

A335259 Triangle read by rows: T(n,k) = k^ceiling(n/k) for 1 <= k <= n.

Original entry on oeis.org

1, 1, 2, 1, 4, 3, 1, 4, 9, 4, 1, 8, 9, 16, 5, 1, 8, 9, 16, 25, 6, 1, 16, 27, 16, 25, 36, 7, 1, 16, 27, 16, 25, 36, 49, 8, 1, 32, 27, 64, 25, 36, 49, 64, 9, 1, 32, 81, 64, 25, 36, 49, 64, 81, 10, 1, 64, 81, 64, 125, 36, 49, 64, 81, 100, 11, 1, 64, 81, 64, 125, 36, 49, 64, 81, 100, 121, 12

Offset: 1

Dennis P. Walsh, May 28 2020

T(n,k) is the number of functions f:[n]->[k] such that f(x)=f(y) whenever i*k-k+1<=x<=y<=i*k where 1<=i<=ceiling(n/k). An example of such a function is f:[8]->[3] defined by f(1)=f(2)=f(3)=2, f(4)=f(5)=f(6)=3, and f(7)=f(8)=2. To count all functions of this type when n=8 and k=3, we note that there are 3 possible values for f(1), f(4), and f(7). Hence T(8,3)=3^3 or, equivalently, 3^ceiling(8/3). A proof of the general result follows the same approach. We also note the following: (i) T(n,1)=1 for all n; (ii) T(n,n)=n for all n; T(n,k)=k^2 when ceiling(n/2)<=k

			Triangle T(n,k):
  1;
  1,  2;
  1,  4,  3;
  1,  4,  9,  4;
  1,  8,  9, 16,  5;
  1,  8,  9, 16, 25,  6;
  1, 16, 27, 16, 25, 36,  7;
  1, 16, 27, 16, 25, 36, 49,  8;
  1, 32, 27, 64, 25, 36, 49, 64,  9;
  1, 32, 81, 64, 25, 36, 49, 64, 81, 10;
...
T(8,3) counts the 27 functions from [8] to [3] where f(1)=f(2)=f(3), f(4)=f(5)=f(6), and f(7)=f(8). Letting f be defined by its vector of images <f(1), ...,f(8)>, the 27 functions are <1,1,1,1,1,1,1,1>, <1,1,1,1,1,1,2,2>, <1,1,1,1,1,1,3,3>, <1,1,1,2,2,2,1,1>, <1,1,1,2,2,2,2,2>, <1,1,1,2,2,2,3,3>, <1,1,1,3,3,3,1,1>, <1,1,1,3,3,3,2,2>, <1,1,1,3,3,3,3,3>, <2,2,2,1,1,1,1,1>, <2,2,2,1,1,1,2,2>, <2,2,2,1,1,1,3,3>, <2,2,2,2,2,2,1,1>, <2,2,2,2,2,2,2,2>, <2,2,2,2,2,2,3,3>, <2,2,2,3,3,3,1,1>, <2,2,2,3,3,3,2,2>, <2,2,2,3,3,3,3,3>, <3,3,3,1,1,1,1,1>, <3,3,3,1,1,1,2,2>, <3,3,3,1,1,1,3,3>, <3,3,3,2,2,2,1,1>, <3,3,3,2,2,2,2,2>, <3,3,3,2,2,2,3,3>, <3,3,3,3,3,3,1,1>, <3,3,3,3,3,3,2,2>, and <3,3,3,3,3,3,3,3>.

Cf. A016116, A127975.

Maple
```
seq(seq(k^ceil(n/k),k=1..n),n=1..20);
```

Table[k^Ceiling[n/k], {n, 12}, {k, n}] // Flatten (* Michael De Vlieger, Jun 28 2020 *)

G.f. for fixed k: k*x^k*(1+k*x+k*x^2+...+k*x^(k-1))/(1-k*x^k).
For n>1, T(n,2) = A016116(n).
For n>2, T(n,3) = A127975(n).

Showing 1-5 of 5 results.

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A111575 Powers of 3 repeated four times.

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A127974 Numerators in expansion of (1-x)^(-2/3).

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A242763 a(n) = 1 for n <= 7; a(n) = a(n-5) + a(n-7) for n>7.

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A335259 Triangle read by rows: T(n,k) = k^ceiling(n/k) for 1 <= k <= n.

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