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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A197819 Table of binary Walsh functions w(A001317), columns read as binary numbers.

Original entry on oeis.org

0, 1, 0, 3, 2, 1, 0, 15, 10, 5, 12, 3, 6, 9, 8, 7, 2, 13, 4, 11, 14, 1, 0, 255, 170, 85, 204, 51, 102, 153, 136, 119, 34, 221, 68, 187, 238, 17, 240, 15, 90, 165, 60, 195, 150, 105, 120, 135, 210, 45, 180, 75, 30, 225, 160, 95, 10, 245, 108, 147
Offset: 0

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Author

Tilman Piesk, Oct 18 2011, reviewed Aug 25 2013

Keywords

Comments

The rows of an infinite binary Walsh matrix (compare A228539) are the binary Walsh functions w(0),w(1),w(2),w(3),...
This number triangle represents the infinite binary array w(1),w(3),w(5),w(15),... (1,3,5,15,... is A001317.)
T(n,k) is column k of the (2^n) X (2^2^n) submatrix read as a binary number.
Top left 4 X 16 submatrix of the binary array:
0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1
0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0
0 1 0 1 1 0 1 0 0 1 0 1 1 0 1 0
0 1 1 0 1 0 0 1 1 0 0 1 0 1 1 0
In the sequence this is represented by row 2:
0 15 10 5 12 3 6 9 8 7 2 13 4 11 14 1
A195467 is the infinite array of Gray code permutation powers. It can be defined by this binary array, which happens to be A195467 mod 2.
Each odd column is the complement of the even column on its left.
Each row of the number triangle is a self-inverse Walsh permutation. The subsequence of even entries (on the even places) divided by 2 is a self-inverse Walsh permutation too.

Crossrefs

Cf. A195467 (consecutive powers of the Gray code permutation).
Cf. A001317 (Sierpinski triangle rows read like binary numbers).

A195608 Numbers n such that Sum_{i=1..n} A(i) = A(n)*A(n+1)/4, where A(n) = A001969(n).

Original entry on oeis.org

1, 7, 11, 12, 13, 19, 20, 21, 25, 31, 35, 36, 37, 41, 47, 48, 49, 55, 59, 60, 61, 67, 68, 69, 73, 79, 80, 81, 87, 91, 92, 93, 97, 103, 107, 108, 109, 115, 116, 117, 121, 127, 131, 132, 133, 137, 143, 144, 145, 151, 155, 156, 157, 161, 167, 171, 172, 173, 179
Offset: 1

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Author

Vladimir Shevelev, Sep 21 2011

Keywords

Comments

Conjectures: 1) there are only 3 different first differences 1,4,6; 2) the sequence contains either isolated series of terms, e.g., {1},{7},{25},{31},..., or series of 3 consecutive integers, e.g., {11,12,13}, {19,20,21}, etc.; 3)the first terms m of every series satisfy the condition A(m+1)-A(m-1)=5, where A(n)=A001969(n).

Crossrefs

Programs

  • Mathematica
    a = Select[Range[0, 1000], EvenQ[DigitCount[#, 2][[1]]] &]; t = {}; s = 0; Do[s = s + a[[n]]; If[s == a[[n]] a[[n + 1]]/4, AppendTo[t, n]], {n, Length[a] - 1}]; t (* T. D. Noe, Sep 23 2011 *)
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