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.

Previous Showing 11-20 of 35 results. Next

A013620 Triangle of coefficients in expansion of (2+3x)^n.

Original entry on oeis.org

1, 2, 3, 4, 12, 9, 8, 36, 54, 27, 16, 96, 216, 216, 81, 32, 240, 720, 1080, 810, 243, 64, 576, 2160, 4320, 4860, 2916, 729, 128, 1344, 6048, 15120, 22680, 20412, 10206, 2187, 256, 3072, 16128, 48384, 90720, 108864, 81648, 34992, 6561, 512
Offset: 0

Views

Author

Keywords

Comments

Row sums give A000351; central terms give A119309. - Reinhard Zumkeller, May 14 2006

Examples

			Triangle begins:
1;
2,3;
4,12,9;
8,36,54,27;
16,96,216,216,81;
		

Crossrefs

Programs

  • Haskell
    a013620 n k = a013620_tabl !! n !! k
    a013620_row n = a013620_tabl !! n
    a013620_tabl = iterate (\row ->
       zipWith (+) (map (* 2) (row ++ [0])) (map (* 3) ([0] ++ row))) [1]
    -- Reinhard Zumkeller, May 26 2013, Apr 02 2011
  • Mathematica
    Flatten[Table[Binomial[i, j] 2^(i-j) 3^j, {i, 0, 10}, {j, 0, i}]] (* Vincenzo Librandi, Apr 22 2014 *)

Formula

G.f.: 1 / [1 - x(2+3y)].
T(n,k) = A007318(n,k) * A036561(n,k). - Reinhard Zumkeller, May 14 2006

A038220 Triangle whose (i,j)-th entry is binomial(i,j)*3^(i-j)*2^j.

Original entry on oeis.org

1, 3, 2, 9, 12, 4, 27, 54, 36, 8, 81, 216, 216, 96, 16, 243, 810, 1080, 720, 240, 32, 729, 2916, 4860, 4320, 2160, 576, 64, 2187, 10206, 20412, 22680, 15120, 6048, 1344, 128, 6561, 34992, 81648, 108864, 90720, 48384, 16128, 3072, 256
Offset: 0

Views

Author

Keywords

Comments

Row sums give A000351; central terms give A119309. - Reinhard Zumkeller, May 14 2006
Triangle of coefficients in expansion of (3 + 2x)^n, where n is a nonnegative integer. - Zagros Lalo, Jul 23 2018

Examples

			Triangle begins:
   1;
   3,   2;
   9,  12,   4;
  27,  54,  36,   8;
  81, 216, 216,  96,  16;
  ...
		

References

  • Shara Lalo and Zagros Lalo, Polynomial Expansion Theorems and Number Triangles, Zana Publishing, 2018, ISBN: 978-1-9995914-0-3, pp. 44, 48

Crossrefs

Programs

  • Haskell
    a038220 n k = a038220_tabl !! n !! k
    a038220_row n = a038220_tabl !! n
    a038220_tabl = iterate (\row ->
       zipWith (+) (map (* 3) (row ++ [0])) (map (* 2) ([0] ++ row))) [1]
    -- Reinhard Zumkeller, May 26 2013, Apr 02 2011
    
  • Mathematica
    t[0, 0] = 1; t[n_, k_] := t[n, k] = If[n < 0 || k < 0, 0, 3 t[n - 1, k] + 2 t[n - 1, k - 1]]; Table[t[n, k], {n, 0, 9}, {k, 0, n}] // Flatten (* Zagros Lalo, Jul 23 2018 *)
    Table[CoefficientList[ Expand[(3 + 2x)^n], x], {n, 0, 9}] // Flatten  (* Zagros Lalo, Jul 23 2018 *)
    Table[CoefficientList[Binomial[i, j] *3^(i - j)*2^j, x], {i, 0, 9}, {j, 0, i}] // Flatten (* Zagros Lalo, Jul 23 2018 *)
  • PARI
    T(i,j)=binomial(i,j)*3^(i-j)*2^j \\ Charles R Greathouse IV, Jul 19 2016

Formula

T(n,k) = A007318(n,k) * A036561(n,k). - Reinhard Zumkeller, May 14 2006
G.f.: 1/(1 - 3*x - 2*x*y). - Ilya Gutkovskiy, Apr 21 2017
T(0,0) = 1; T(n,k) = 3 T(n-1,k) + 2 T(n-1,k-1) for k = 0...n; T(n,k)=0 for n or k < 0. - Zagros Lalo, Jul 23 2018

A087465 Rank array R of 3/2 read by antidiagonals; this array is the dispersion of the complement of the sequence given by r(n) = r(n-1) + 1 + floor(3n/2) for n>=1, with r(0) = 1; that is, A077043(n+1).

Original entry on oeis.org

1, 2, 3, 4, 5, 7, 6, 8, 10, 12, 9, 11, 14, 16, 19, 13, 15, 18, 21, 24, 27, 17, 20, 23, 26, 30, 33, 37, 22, 25, 29, 32, 36, 40, 44, 48, 28, 31, 35, 39, 43, 47, 52, 56, 61, 34, 38, 42, 46, 51, 55, 60, 65, 70, 75, 41, 45, 50, 54, 59, 64, 69, 74, 80, 85, 91, 49, 53, 58, 63, 68, 73
Offset: 0

Views

Author

Clark Kimberling, Sep 09 2003

Keywords

Comments

The sequence is a permutation of the positive integers and the array is a transposable dispersion.
Let T(n,k) be the rectangular version of the array at A036561, with northwest corner as shown here:
1 2 4 8 16 32
3 6 12 24 48 96
9 18 36 72 144 288
27 54 108 216 432 864
Then R(n,k) is the rank of T(n,k) when all the numbers in {T(n,k)} are jointly ranked. - Clark Kimberling, Jan 25 2018

Examples

			Northwest corner of R:
   1    2    4    6    9   13   17   22
   3    5    8   11   15   20   25   31
   7   10   14   18   23   29   35   42
  12   16   21   26   32   39   46   54
  19   24   30   36   43   51   59   68
  27   33   40   47   55   64   73   83
  37   44   52   60   69   79   89  100
Let t=3/2; then R(i,j) = rank of (j,i) when all nonnegative integer pairs (a,b) are ranked by the relation << defined as follows: (a,b) << (c,d) if a + b*t < c + d*t, and also (a,b) << (c,d) if a + b*t = c + d*t and b < d.  Thus R(2,1) = 10 is the rank of (1,2) in the list (0,0) << (1,0) << (0,1) << (2,0) << (1,1) << (3,0) << (0,2) << (2,1) << (4,0) << (1,2).
		

Crossrefs

Cf. A087466, A087468, A087483, A007780 (row 1), A077043 (column 1).

Programs

  • Mathematica
    r = 20; r1 = 12;(*r=# rows of T,r1=# rows to show*);
    c = 20; c1 = 12;(*c=# cols of T,c1=# cols to show*);
    s[0] = 1; s[n_] := s[n] = s[n - 1] + 1 + Floor[3 n/2]; u = Table[s[n], {n, 0, 100}]
    v = Complement[Range[Max[u]], u]; f[n_] := v[[n]]; Table[f[n], {n, 1, 30}]
    mex[list_] := NestWhile[#1 + 1 &, 1, Union[list][[#1]] <= #1 &, 1,   Length[Union[list]]]; rows = {NestList[f, 1, c]}; Do[rows = Append[rows, NestList[f, mex[Flatten[rows]], r]], {r}]; w[i_, j_] := rows[[i, j]];
    TableForm[Table[w[i, j], {i, 1, 10}, {j, 1, 10}]]   (* A087465 array *)
    Flatten[Table[w[k, n - k + 1], {n, 1, c1}, {k, 1, n}]] (* A087465 sequence *)
    TableForm[Table[w[i, 1] + w[1, j] + (i - 1)*(j - 1) - 1, {i, 1, 10}, {j, 1, 10}]] (* A087465 array, by formula *)

Formula

R(i,j) = R(i,0) + R(0,j) + i*j - 1, for i>=1, j>=1.

Extensions

Updated by Clark Kimberling, Sep 23 2014

A180845 a(n) = (16^n-3^n)/13.

Original entry on oeis.org

0, 1, 19, 313, 5035, 80641, 1290499, 20648713, 330381595, 5286112081, 84577812979, 1353245066713, 21651921244555, 346430740444321, 5542891848703459, 88686269584038313, 1418980313358961915
Offset: 0

Views

Author

Johannes W. Meijer, Sep 21 2010

Keywords

Comments

The a(n+1) appear in several triangle sums of Nicomachus' table A036561, i.e Gi1(4*n), Gi1(4*n+1)/2, Gi1(4*n+2)/4, Gi1(4*n+3)/8 and Gi4(n). See A180662 for information about these giraffe and other chess sums.

Crossrefs

Programs

Formula

a(n) = (16^n-3^n)/13
G.f.: x/((16*x-1)*(3*x-1))

A180844 a(n) = (27^n - 2^n)/25.

Original entry on oeis.org

0, 1, 29, 787, 21257, 573955, 15496817, 418414123, 11297181449, 305023899379, 8235645283745, 222362422662139, 6003785411879801, 162102206120758723, 4376759565260493713, 118172508262033346635, 3190657723074900391913
Offset: 0

Views

Author

Johannes W. Meijer, Sep 21 2010

Keywords

Comments

The a(n+1) appear in several triangle sums of Nicomachus's table A036561, i.e., Ca2(3*n), Ca2(3*n+1)/3, Ca2(3*n+2)/9 and Ca3(n). See A180662 for information about these camel sums and other chess sums.

Crossrefs

Programs

  • Mathematica
    (#[[1]]-#[[2]])/25&/@Partition[Riffle[27^Range[0,20],2^Range[0,20]],2]  (* Harvey P. Dale, Jan 22 2011 *)
  • PARI
    a(n) = (27^n - 2^n)/25 \\ Iain Fox, Dec 12 2017
    
  • PARI
    first(n) = Vec(x/((27*x-1)*(2*x-1)) + O(x^n), -n) \\ Iain Fox, Dec 12 2017

Formula

a(n) = (27^n - 2^n)/25.
G.f.: x/((27*x-1)*(2*x-1)).

A180846 a(n) = (81^n - 2^n)/79.

Original entry on oeis.org

0, 1, 83, 6727, 544895, 44136511, 3575057423, 289579651327, 23455951757615, 1899932092367071, 153894499481733263, 12465454458020395327, 1009701811099652023535, 81785846699071813910431, 6624653582624816926753103
Offset: 0

Views

Author

Johannes W. Meijer, Sep 21 2010

Keywords

Comments

The a(n+1) appear in several triangle sums of Nicomachus's table A036561, i.e., Gi2(4*n), Gi2(4*n+1)/2, Gi2(4*n+2)/4, Gi2(4*n+3)/8 and Gi3(n). See A180662 for information about these giraffe and other chess sums.

Crossrefs

Programs

Formula

a(n) = (81^n - 2^n)/79.
G.f.: x/((81*x-1)*(2*x-1)).

A180847 a(n) = (27^n-4^n)/23.

Original entry on oeis.org

0, 1, 31, 853, 23095, 623821, 16844191, 454797253, 12279542215, 331547705341, 8951788306351, 241698285320053, 6525853707835735, 176198050128342061, 4757347353532344511, 128448378545641737253, 3468106220733400647655
Offset: 0

Views

Author

Johannes W. Meijer, Sep 21 2010

Keywords

Comments

For n>0, a(n) appears in several triangle sums of Nicomachus' table A036561, i.e. Ze1(2*n), Ze1(2*n+1)/2; Ze4(3*n), Ze4(3*n+1)/3 and Ze4(3*n+2)/9. See A180662 for information about these zebra and other chess sums.

Crossrefs

Programs

  • Mathematica
    Table[(27^n-4^n)/23,{n,0,20}] (* or *) LinearRecurrence[{31,-108},{0,1},20]  (* Harvey P. Dale, Sep 01 2011 *)
  • PARI
    a(n)=(27^n-4^n)/23 \\ Charles R Greathouse IV, Oct 07 2015

Formula

a(n) = (27^n-4^n)/23.
G.f.: x/((27*x-1)*(4*x-1)).
a(0)=0, a(1)=1, a(n) = 31*a(n-1)-108*a(n-2). - Harvey P. Dale, Sep 01 2011

A164057 Complement to A164056, change A164056 bits (0->1; 1->0). Provides a coding template for Petoukhov matrices, relating to DNA codons.

Original entry on oeis.org

1, 1, 0, 1, 0, 0, 1, 1, 0, 0, 1, 0, 0, 1, 1, 1, 0, 0, 1, 0, 0, 1, 1, 0, 0, 0, 1, 1, 0, 1, 1, 1, 0, 0, 1, 0, 0, 1, 1, 0, 0, 0, 1, 1, 0, 1, 1
Offset: 0

Views

Author

Gary W. Adamson, Aug 09 2009

Keywords

Comments

Sequences by rows can be used as mapping tools for generating Gray code maps.
Jay Kappraff alerted me to the connection between the multiplication version (below) and the 2*3 multiplication table of A036561, in that the terms of the multiplication table (below): (27, 18, 12, 8) are seen as a diagonal in:
1...3,...9,...27,...
2,..6,..18,.........
4..12...............
8...................
.
We may recreate the top row (below): (27, 18, 12, 18, 12, 8, 12, 18), by starting at "27" in the above array, then given the code (1,0,0,1,0,0,1,1), and (8, 12, 18, 27), we mark down the term to the left if the code = 0, (1 otherwise), giving "27" then L,L,R,L,L,R,R or: (27, 18, 12, 18, 12, 8, 12, 18).
Such operations preserve the harmonic character of the isomorphic array in terms of multiplication or division by (2/3) or (3/2) linked to the 2*3 multiplication table. The Gray code map preserves the "one operation" procedure as well as a binomial distribution as to frequency.
The 8*8 array below with top row [27, 18, 12, 18, 12, 8, 12, 18]... has been investigated extensively by Petoukhov, relating to the 64 DNA codons (Cf. A164091, A147995). Petoukhov has made the remarkable discovery that such (Petoukhov matrices) can be generated as squares of matrices with irrational terms, in this case phi, 1.618...

Examples

			First few rows of the triangle in 2^n term strings:
1;
1, 0;
1, 0, 0, 1;
1, 0, 0, 1, 0, 0, 1, 1;
1, 0, 0, 1, 0, 0, 1, 1, 0, 0, 0, 1, 1, 0, 1, 1;
...
Given the 16 bit Gray code string (0,...->15): 0000, 0001, 0011, 0010, 0110, 0111, 0101, 0100, 1100, 1101, 1111, 1110, 1010, 1011, 1001, 1000; the number f of 1's per term = (0, 1, 2, 1, 2, 3, 2, 1, 2, 3, 4, 3, 2, 3, 2, 1). Then using the increase/decrease rule, we get row 5 of A164056
.
0, 1, 1, 0, 1, 1, 0, 0, 1, 1, 1, 0, 0, 1, 0, 0 = row 5 of A164056.
Change to
1, 0, 0, 1, 0, 0, 1, 1, 0, 0, 0, 1, 1, 0, 1, 1 = row 5 of A164057.
.
We may use row 3 to generate arrays that make use of the terms by addition or multiplication: By addition: we recreate an array of the number of hydrogen bonds per codon/anti-codon (Cf. A147995, the 64 codons mapped on a Gray code format). Beginning with "9" and using row 4: (1,0,0,1,0,0,1,1); we increase by 1 starting from left if we encounter a 1, and decrease by 1 if the next term = 0. We get: (9, 8, 7, 8, 7, 6, 7, 8) = A. Next, the same sequence A along the left border and 9's as the diagonal. Given upper left term = (1,1), for odd numbered columns (n), begin at position (n,n) and circulate A downward. For even numbered columns, circulate A upward.
This gets us:
.
9, 8, 7, 8, 7, 6, 7, 8
8, 9, 8, 7, 6, 7, 8, 7
7, 8, 9, 8, 7, 8, 7, 6
8, 7, 8, 9, 8, 7, 8, 7
7, 6, 7, 8, 9, 8, 7, 8
6, 7, 8, 7, 8, 9, 6, 7
7, 8, 7, 6, 7, 8, 9, 8
8, 7, 6, 7, 8, 7, 8, 9
.
As shown, (for example), column 4 begins at (4,4), then circulates upwards with sequence A. Last, we superimpose the hydrogen bond array on the DNA array as shown in A147995. Mapping the terms according to the Gray code rules preserves the "1" rule in any Knights's move direction including wrap-arounds: Every neighbor differs from any entry by "1" by addition or subtraction.
Note that in the previous array, (6, 7, 8, 9) may be obtained by the appropriate addition of terms (2 or 3). In the next example, we use the rows to generate A164091, (which I name Petoukhov matrices) as follows:
.
Again, we refer to row 5: (1, 0, 0, 1, 0, 0, 1, 1) and given the upper left term of an 8x8 array = (1,1), we begin with "27" (= 3*3*3 rather than 3+3+3 = 9 as in the addition case. Then, when encountering an 0, multiply current term by (2/3). If the next term = 1, multiply current term by (3/2). Then use the identical circulate rule using "B" = (27, 18, 12, 18, 12, 8, 12, 18) since given (1, 0, 0, 1, 0, 0, 1, 1) and "27", the next term (an 18) = (2/3) * 27, followed by 12 = (2/3)*18, etc; getting: (Cf. A164091):
.
27, 18, 12, 18, 12, 08, 12, 18
18, 27, 18, 12, 08, 12, 18, 12
12, 18, 27, 18, 12, 18, 12, 08
18, 12, 18, 27, 18, 12, 08, 12
12, 08, 12, 18, 27, 18, 12, 18
08, 12, 18, 12, 18, 27, 18, 12
12, 18, 12, 08, 12, 18, 27, 18
18, 12, 08, 12, 18, 12, 18, 27
.
Both the addition case and the multiplication case have a binomial frequency of terms by rows and columns: (one 9, three 7's, three 8's and one 6); while the multiplication case has (one 27, three 18's three 12's and one 8). Both versions preserve the Gray code "one operation" rule in any Knight's move including wrap arounds, since given the second case, any neighbor may be obtained by multiplication of (2/3) or (3/2).
		

References

  • Sergei Petoukhov and Matthew He, "Symmetrical Analysis Techniques for Genetic Systems and Bioinformatics - Advanced Patterns and Applications", IGI Global, (978-1-60566-127-9); October, 2009, Chapters (2, 4, and 6) Clifford Pickover, "The Zen of Magic Squares, Circles, and Stars", Princeton University Press, 2002, pages 285-289.

Crossrefs

Formula

By rows, change bits of A164056: (0->1); (1->0). Note that A164056 can be derived from 2^n strings of Gray code terms by recording the number of 1's in the Gray code terms for n, followed by the rule "1" is recorded if next term is greater than current; 0 otherwise.

A094617 Triangular array T of numbers generated by these rules: 2 is in T; and if x is in T, then 2x-1 and 3x-2 are in T.

Original entry on oeis.org

2, 3, 4, 5, 7, 10, 9, 13, 19, 28, 17, 25, 37, 55, 82, 33, 49, 73, 109, 163, 244, 65, 97, 145, 217, 325, 487, 730, 129, 193, 289, 433, 649, 973, 1459, 2188, 257, 385, 577, 865, 1297, 1945, 2917, 4375, 6562, 513, 769, 1153, 1729, 2593, 3889, 5833, 8749, 13123, 19684
Offset: 1

Views

Author

Clark Kimberling, May 14 2004

Keywords

Comments

To obtain row n from row n-1, apply 2x-1 to each x in row n-1 and then put 1+3^n at the end. Or, instead, apply 3x-2 to each x in row n-1 and then put 1+2^n at the beginning.
From Lamine Ngom, Feb 10 2021: (Start)
Triangle read by diagonals provides all the sequences of the form 1+2^(k-1)*3^n, where k is the k-th diagonal.
For instance, the terms of the first diagonal form the sequence 2, 4, 10, 28, ..., i.e., 1+3^n (A034472).
The 2nd diagonal leads to the sequence 3, 7, 19, 55, ..., i.e., 1+2*3^n (A052919).
The 3rd diagonal is the sequence 5, 13, 37, 109, ..., i.e., 1+4*3^n (A199108).
And for k = 4, we obtain the sequence 9, 25, 73, 217, ..., i.e., 1+8*3^n (A199111). (End)

Examples

			Rows of this triangle begin:
    2;
    3,   4;
    5,   7,   10;
    9,  13,   19,   28;
   17,  25,   37,   55,   82;
   33,  49,   73,  109,  163,  244;
   65,  97,  145,  217,  325,  487,  730;
  129, 193,  289,  433,  649,  973, 1459, 2188;
  257, 385,  577,  865, 1297, 1945, 2917, 4375,  6562;
  513, 769, 1153, 1729, 2593, 3889, 5833, 8749, 13123, 19684;
  ...
		

Crossrefs

Programs

  • Mathematica
    FoldList[Append[2 #1 - 1, 1 + 3^#2] &, {2}, Range[9]] // Flatten (* Ivan Neretin, Mar 30 2016 *)

Formula

When offset is zero, then the first term is T(0,0) = 2, and
T(n,0) = 1 + 2^n = A000051(n),
T(n,n) = 1 + 3^n = A048473(n),
T(2n,n) = 1 + 6^n = A062394(n).
Row sums = A094618.
a(n) = A036561(n-1) + 1. - Filip Zaludek, Nov 19 2016

A163892 Distinct values in A163890 in the order of appearance.

Original entry on oeis.org

1, 2, 6, 3, 4, 8, 12, 18, 9, 16, 32, 24, 108, 36, 48, 54, 72, 64, 96, 192, 216, 324, 144, 162, 288, 576, 648, 384, 1944, 432, 864, 486, 972, 1296, 27, 768, 1152, 128, 5832, 1728, 1536, 3456, 2304
Offset: 0

Views

Author

Antti Karttunen, Sep 19 2009

Keywords

Comments

Probably a permutation of A003586 (A036561).

Crossrefs

a(n) = A163890(A163891(n)). See also A163891, A163893, A163894, A163912.
Previous Showing 11-20 of 35 results. Next