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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A057115 Order-preserving permutation of the rational numbers (x -> x-1); positions in Stern-Brocot tree.

Original entry on oeis.org

2, 4, 1, 8, 9, 5, 3, 16, 17, 18, 19, 10, 11, 6, 7, 32, 33, 34, 35, 36, 37, 38, 39, 20, 21, 22, 23, 12, 13, 14, 15, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 40, 41, 42, 43, 44, 45, 46, 47, 24, 25, 26, 27, 28, 29, 30, 31, 128, 129, 130, 131, 132, 133, 134, 135, 136, 137, 138, 139, 140, 141, 142, 143, 144, 145, 146, 147, 148, 149, 150
Offset: 1

Views

Author

Antti Karttunen, Aug 09 2000

Keywords

Crossrefs

Inverse permutation: A057114.
When conjugated with A059893, one gets A065260, a valid siteswap permutation.
The first row of A065626, i.e. a(n) = RotateNodeLeft(1, n).

Programs

  • Maple
    sbtree_perm_1_1_left := x -> (`if`((x <= 0),x,(`if`((x < 1),(x/(1+x)),(`if`((x < 2),(1/(3-x)),(x-1)))))));

Formula

a(n) = frac2position_in_whole_SB_tree(sbtree_perm_1_1_left(SternBrocotTreeNum(n)/SternBrocotTreeDen(n)))

A139708 Take n in binary. Rotate the binary digits to the left until a 1 once again appears as the leftmost digit. Convert back into decimal for a(n).

Original entry on oeis.org

1, 2, 3, 4, 6, 5, 7, 8, 12, 10, 14, 9, 11, 13, 15, 16, 24, 20, 28, 18, 22, 26, 30, 17, 19, 21, 23, 25, 27, 29, 31, 32, 48, 40, 56, 36, 44, 52, 60, 34, 38, 42, 46, 50, 54, 58, 62, 33, 35, 37, 39, 41, 43, 45, 47, 49, 51, 53, 55, 57, 59, 61, 63, 64, 96, 80, 112, 72, 88, 104, 120
Offset: 1

Views

Author

Leroy Quet, Apr 30 2008

Keywords

Comments

This sequence written in binary is A139709.
This is a permutation of the positive integers. A139706 is the inverse permutation.
Moreover, the first 2^n terms are a permutation of the first 2^n positive integers. Fixed points of the permutation are A272919. - Ivan Neretin, May 10 2016

References

  • Lionel Levine, Fractal sequences and restricted Nim, Ars Combin. 80 (2006), 113-127.

Crossrefs

Cf. A139706 (inverse), A139709 (in binary), A272919 (fixed points).

Programs

  • Maple
    A139708 := proc(n) local a; a := ListTools[Rotate](convert(n,base,2),-1) ; while op(-1,a) = 0 do a := ListTools[Rotate](a,-1) ; od: add(op(i,a)*2^(i-1),i=1..nops(a)) : end: seq(A139708(n),n=1..100) ; # R. J. Mathar, May 04 2008
  • Mathematica
    rbd[n_]:=Module[{idn2=RotateLeft[IntegerDigits[n,2]]},While[ idn2[[1]] ==0, idn2= RotateLeft[ idn2]];FromDigits[idn2,2]]; Array[rbd,80] (* Harvey P. Dale, Jun 07 2015 *)
    Table[FromDigits[RotateLeft[d = IntegerDigits[n, 2], Position[Join[d, d], 1][[2, 1]] - 1], 2], {n, 71}] (* Ivan Neretin, May 10 2016 *)
  • PARI
    a(n) = if(bitand(n,n-1)==0, n, my(b=logint(n,2), s=b-logint(n-(1<Andrew Howroyd, Jan 04 2024

Formula

From Mikhail Kurkov, Dec 23 2023: (Start)
a(2^m + k) = f(2^m + f(k)) for m >= 0, 0 <= k < 2^m where f(n) = A059893(n) for n > 0 with f(0) = 0.
a(n) = f(A139706(f(n))). (End)

Extensions

More terms from R. J. Mathar, May 04 2008

A153151 Rotated binary decrementing: For n<2 a(n) = n, if n=2^k, a(n) = 2*n-1, otherwise a(n) = n-1.

Original entry on oeis.org

0, 1, 3, 2, 7, 4, 5, 6, 15, 8, 9, 10, 11, 12, 13, 14, 31, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 63, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 127, 64, 65, 66, 67, 68, 69
Offset: 0

Views

Author

Antti Karttunen, Dec 20 2008

Keywords

Comments

Without the initial 0, a(n) is the lexicographically minimal sequence of distinct positive integers such that all values of a(n) mod n are distinct and nonnegative. - Ivan Neretin, Apr 27 2015
A002487(n)/A002487(n+1), n > 0, runs through all the reduced nonnegative rationals exactly once. A002487 is the Stern's sequence. Permutation from denominators (A002487(n+1))
1 2 1 3 2 3 1 4 3 5 2 5 3 4 1
where labels are
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
to numerators (A002487(n))
1 1 2 1 3 2 3 1 4 3 5 2 5 3 4
where changed labels are
1 3 2 7 4 5 6 15 8 9 10 11 12 13 14
Thus, b(n) = A002487(n+1), b(a(n)) = A002487(n), n>0. - Yosu Yurramendi, Jul 07 2016

Crossrefs

Programs

  • Maple
    a := n -> if n < 2 then n elif convert(convert(n, base, 2), `+`) = 1 then 2*n-1 else n-1 fi: seq(a(n), n=0..70); # Peter Luschny, Jul 16 2016
  • Mathematica
    Table[Which[n < 2, n, IntegerQ[Log[2, n]], 2 n - 1, True, n - 1], {n, 0, 70}] (* Michael De Vlieger, Apr 27 2015 *)
  • Python
    def ok(n): return n&(n - 1)==0
    def a(n): return n if n<2 else 2*n - 1 if ok(n) else n - 1 # Indranil Ghosh, Jun 09 2017
    
  • R
    nmax <- 126 # by choice
    a <- c(1,3,2)
    for(n in 3:nmax) a[n+1] <- n
    for(m in 0:floor(log2(nmax))) a[2^m] <- 2^(m+1) - 1
    a <- c(0, a)
    # Yosu Yurramendi, Sep 05 2020

Formula

A268087 a(n) = A162909(n) + A162910(n).

Original entry on oeis.org

2, 3, 3, 5, 4, 4, 5, 8, 7, 5, 7, 7, 5, 7, 8, 13, 11, 9, 12, 9, 6, 10, 11, 11, 10, 6, 9, 12, 9, 11, 13, 21, 18, 14, 19, 16, 11, 17, 19, 14, 13, 7, 11, 17, 13, 15, 18, 18, 15, 13, 17, 11, 7, 13, 14, 19, 17, 11, 16, 19, 14, 18, 21, 34, 29, 23, 31, 25, 17, 27, 30, 25, 23, 13, 20, 29, 22, 26, 31, 23, 19, 17, 22, 13, 8, 16, 17, 27
Offset: 1

Views

Author

Yosu Yurramendi, Jan 26 2016

Keywords

Comments

If the terms (n>0) are written as an array (in a left-aligned fashion) with rows of length 2^m, m >= 0:
2,
3, 3,
5, 4, 4, 5,
8, 7, 5, 7, 7, 5, 7, 8,
13,11, 9,12, 9, 6,10,11,11,10,6, 9,12, 9,11,13,
21,18,14,19,16,11,17,19,14,13,7,11,17,13,15,18,18,15,13,17,11,7,13,14,19,17,11,16, ...
a(n) is palindromic in each level m >= 0 (ranks between 2^m and 2^(m+1)-1), because in each level m >= 0 A162910 is the reverse of A162909:
a(2^m + k) = a(2^(m+1) - 1 - k), m >= 0, 0 <= k < 2^m.
All columns have the Fibonacci sequence property: a(2^(m+2) + k) = a(2^(m+1) + k) + a(2^m + k), m >= 0, 0 <= k < 2^m (empirical observations).
a(2^m + k) = A162909(2^(m+2) + k), a(2^m + k) = A162909(2^(m+1)+ 2^m + k), a(2^m + k) = A162910(2^(m+1) + k), m >= 0, 0 <= k < 2^m (empirical observations).
a(n) = A162911(n) + A162912(n), where A162911(n)/A162912(n) is the bit reversal permutation of A162909(n)/A162910(n) in each level m >= 0 (empirical observations).
a(n) = A162911(2n+1), a(n) = A162912(2n) for n > 0 (empirical observations). n > 1 occurs in this sequence phi(n) = A000010(n) times, as it occurs in A007306 (Franklin T. Adams-Watters's comment), which is the sequence obtained by adding numerator and denominator in the Calkin-Wilf enumeration system of positive rationals. A162909(n)/A162910(n) is also an enumeration system of all positive rationals (Bird system), and in each level m >= 0 (ranks between 2^m and 2^(m+1)-1) rationals are the same in both systems. Thus a(n) has the same terms in each level as A007306.
The same property occurs in all numerator+denominator sequences of enumeration systems of positive rationals, as, for example, A007306 (A007305+A047679), A071585 (A229742+A071766), and A086592 (A020650+A020651).

Examples

			m = 3, k = 6: a(38) = 17, a(22) = 10, a(14) = 7.
		

Crossrefs

Programs

  • PARI
    a(n) = my(x=1, y=1); for(i=0, logint(n, 2), if(bittest(n, i), [x, y]=[x+y, x], [x, y]=[y, x+y])); x \\ Mikhail Kurkov, Mar 10 2023

Formula

a(2^(m+2)+k) = a(2^(m+1)+k) + a(2^m+k) with m = 0, 1, 2, ... and 0 <= k < 2^m (empirical observation).
a(A059893(n)) = a(n) for n > 0. - Yosu Yurramendi, May 30 2017
From Yosu Yurramendi, May 14 2019: (Start)
Take the smallest m > 0 such that 0 <= k < 2^(m-1), and choose any M >= m,
a((1/3)*( A016921(2^(m-1)+k)*4^(M-m)-1)) = 2*a(2^(m-1)+k)*(M-m) + a(2^m+2*k ).
a((1/3)*(2*A016921(2^(m-1)+k)*4^(M-m)-2)) = 2*a(2^(m-1)+k)*(M-m) + a(2^m+2*k ) + a(2^(m-1)+k).
a((1/3)*( A016969(2^(m-1)+k)*4^(M-m)-2)) = 2*a(2^(m-1)+k)*(M-m) + a(2^m+2*k+1).
a((1/3)*(2*A016969(2^(m-1)+k)*4^(M-m)-1)) = 2*a(2^(m-1)+k)*(M-m) + a(2^m+2*k+1) + a(2^(m-1)+k). (End)
a(n) = A007306(A258996(n)), n > 0. - Yosu Yurramendi, Jun 23 2021

A343150 Reverse the order of all but the most significant bits in the minimal Fibonacci expansion of n.

Original entry on oeis.org

1, 2, 3, 4, 5, 7, 6, 8, 11, 10, 9, 12, 13, 18, 16, 15, 20, 14, 19, 17, 21, 29, 26, 24, 32, 23, 31, 28, 22, 30, 27, 25, 33, 34, 47, 42, 39, 52, 37, 50, 45, 36, 49, 44, 41, 54, 35, 48, 43, 40, 53, 38, 51, 46, 55, 76, 68, 63, 84, 60, 81, 73, 58, 79, 71, 66, 87
Offset: 1

Views

Author

J. Parker Shectman, Apr 07 2021

Keywords

Comments

A self-inverse permutation of the natural numbers.
Analogous to A059893 with binary expansion replaced by minimal Fibonacci expansion.
Analogous to A343152 with maximal Fibonacci expansion replaced by minimal Fibonacci expansion.
The expansion of n equals A014417(n) with a 0 appended (see reference in link, p. 144).
Write the sequence as a (left-justified) "tetrangle" or "irregular triangle" tableau with F(t) (Fibonacci number) entries on each row, for t=1,2,3,.... Then, columns of the tableau equal rows of the Wythoff array, A035513 (see reference in link, p. 131):
1
2
3, 4
5, 7, 6
8, 11, 10, 9, 12
13, 18, 16, 15, 20, 14, 19, 17
...

Examples

			For an example of calculation by reversing Fibonacci binary digits, see reference in link, p. 144:
On the basis (1,1,2,3,5,8,13) n=13 is written as 0000001. Reversing all but the most significant digit gives 0000001, which evaluates to 13, so a(13)=13.
On the basis (1,1,2,3,5,8,13) n=14 is written as 0100001. Reversing all but the most significant digit gives 0000101, which evaluates to 18, so a(14)=18.
Note: The permutation can also be accomplished using the basis (1,2,3,5,8,13), by holding fixed the TWO most significant digits and reversing the remaining digits.
		

Crossrefs

In other bases: A344682 (lazy Fibonacci), A343152 (variation), A059893 (binary), A351702 (balanced ternary).

Programs

  • Mathematica
    (*Produce indices of minimal Fibonacci representation (recursively)*)
    MinFibInd[n_] := Module[{t = Floor[Log[GoldenRatio, Sqrt[5]*n + 1]] - 1}, Piecewise[{{{2}, n == 1}, {Append[MinFibInd[n - Fibonacci[t + 1]], t + 1], n > 1 && n - Fibonacci[t + 1] >= Fibonacci[t - 1]}, {Append[Most[MinFibInd[n - Fibonacci[t - 1]]], t + 1], n > 1 && n - Fibonacci[t + 1] < Fibonacci[t - 1]}},]];
    (*Define a(n)*)
    a[n_] := Module[{MFI = MinFibInd[n]}, Apply[Plus, Fibonacci[Append[Last[MFI] - Most[MFI], Last[MFI]]]]];
    (*Generate DATA*)
    Array[a, 67]

A372432 Positive integers k such that the prime indices of k are not disjoint from the binary indices of k.

Original entry on oeis.org

3, 5, 6, 14, 15, 18, 20, 22, 27, 28, 30, 39, 42, 45, 51, 52, 54, 55, 56, 60, 63, 66, 68, 70, 75, 77, 78, 85, 87, 88, 90, 91, 95, 99, 100, 102, 104, 105, 110, 111, 114, 117, 119, 121, 123, 125, 126, 133, 135, 138, 140, 147, 150, 152, 154, 159, 162, 165, 168
Offset: 1

Views

Author

Gus Wiseman, May 03 2024

Keywords

Comments

A binary index of n is any position of a 1 in its reversed binary expansion. The binary indices of n are row n of A048793.
A prime index of n is a number m such that prime(m) divides n. The multiset of prime indices of n is row n of A112798.

Examples

			The binary indices of 18 are {2,5}, and the prime indices are {1,2,2}, so 18 is in the sequence.
The terms together with their prime indices begin:
    3: {2}
    5: {3}
    6: {1,2}
   14: {1,4}
   15: {2,3}
   18: {1,2,2}
   20: {1,1,3}
   22: {1,5}
   27: {2,2,2}
   28: {1,1,4}
   30: {1,2,3}
The terms together with their binary expansions and binary indices begin:
    3:      11 ~ {1,2}
    5:     101 ~ {1,3}
    6:     110 ~ {2,3}
   14:    1110 ~ {2,3,4}
   15:    1111 ~ {1,2,3,4}
   18:   10010 ~ {2,5}
   20:   10100 ~ {3,5}
   22:   10110 ~ {2,3,5}
   27:   11011 ~ {1,2,4,5}
   28:   11100 ~ {3,4,5}
   30:   11110 ~ {2,3,4,5}
		

Crossrefs

For subset instead of overlap we have A372430.
The complement is A372431.
Equal lengths: A071814, zeros of A372441.
Equal sums: A372427, zeros of A372428.
Equal maxima: A372436, zeros of A372442.
A019565 gives Heinz number of binary indices, adjoint A048675.
A029837 gives greatest binary index, least A001511.
A048793 lists binary indices, length A000120, reverse A272020, sum A029931.
A061395 gives greatest prime index, least A055396.
A070939 gives length of binary expansion.
A112798 lists prime indices, length A001222, reverse A296150, sum A056239.

Programs

  • Mathematica
    bix[n_]:=Join@@Position[Reverse[IntegerDigits[n,2]],1];
    prix[n_]:=If[n==1,{},Flatten[Cases[FactorInteger[n],{p_,k_}:>Table[PrimePi[p],{k}]]]];
    Select[Range[100],Intersection[bix[#],prix[#]]!={}&]

A116623 a(0)=1, a(2n) = a(n)+A000079(A000523(2n)), a(2n+1) = 3*a(n) + A000079(A000523(2n+1)+1).

Original entry on oeis.org

1, 5, 7, 19, 11, 29, 23, 65, 19, 49, 37, 103, 31, 85, 73, 211, 35, 89, 65, 179, 53, 143, 119, 341, 47, 125, 101, 287, 89, 251, 227, 665, 67, 169, 121, 331, 97, 259, 211, 601, 85, 223, 175, 493, 151, 421, 373, 1087, 79, 205, 157, 439, 133, 367, 319, 925, 121
Offset: 0

Views

Author

Antti Karttunen, Feb 20 2006. Proposed by Pierre Lamothe (plamothe(AT)aei.ca), May 21 2004

Keywords

Comments

Viewed as a binary tree, this is (1); 5; 7,19; 11,29,23,65; ... Related to the parity vectors of Collatz and Terras trajectories.

Crossrefs

Cf. a(n) = A116640(A059893(n)). a(A000225(n)) = A001047(n+1). For n>= 1 a(A000079(n)) = A062709(n+1). A116641 gives the terms in ascending order and without duplicates.

Programs

  • Maple
    A116623 := proc(n)
        option remember;
        if n = 0 then
            1;
        elif type(n,'even') then
            procname(n/2)+2^A000523(n) ;
        else
            3*procname(floor(n/2))+2^(1+A000523(n)) ;
        end if;
    end proc: # R. J. Mathar, Nov 28 2016
  • Mathematica
    a[n_] := a[n] = Which[n == 0, 1, EvenQ[n], a[n/2] + 2^Floor@Log2[n], True, 3a[Floor[n/2]] + 2^(1 + Floor@Log2[n])];
    Table[a[n], {n, 0, 56}] (* Jean-François Alcover, Sep 01 2023 *)

A359756 First position of n in the sequence of zero-based weighted sums of standard compositions (A124757), if we start with position 0.

Original entry on oeis.org

0, 3, 6, 7, 13, 14, 15, 27, 29, 30, 31, 55, 59, 61, 62, 63, 111, 119, 123, 125, 126
Offset: 0

Views

Author

Gus Wiseman, Jan 17 2023

Keywords

Comments

The k-th composition in standard order (graded reverse-lexicographic, A066099) is obtained by taking the set of positions of 1's in the reversed binary expansion of k, prepending 0, taking first differences, and reversing again. This gives a bijective correspondence between nonnegative integers and integer compositions.
The zero-based weighted sum of a sequence (y_1,...,y_k) is Sum_{i=1..k} (i-1)*y_i.
Is this sequence strictly increasing?

Examples

			The terms together with their standard compositions begin:
    0: ()
    3: (1,1)
    6: (1,2)
    7: (1,1,1)
   13: (1,2,1)
   14: (1,1,2)
   15: (1,1,1,1)
   27: (1,2,1,1)
   29: (1,1,2,1)
   30: (1,1,1,2)
   31: (1,1,1,1,1)
		

Crossrefs

The one-based version is A089633, for prime indices A359682.
First index of n in A124757, reverse A231204.
The version for prime indices is A359676, reverse A359681.
A053632 counts compositions by zero-based weighted sum.
A066099 lists standard compositions.
A304818 gives weighted sums of prime indices, reverse A318283.
A320387 counts multisets by weighted sum, zero-based A359678.

Programs

  • Mathematica
    nn=10;
    stc[n_]:=Differences[Prepend[Join@@Position[Reverse[IntegerDigits[n,2]],1],0]]//Reverse;
    wts[y_]:=Sum[(i-1)*y[[i]],{i,Length[y]}];
    seq=Table[wts[stc[n]],{n,0,2^(nn-1)}];
    Table[Position[seq,k][[1,1]]-1,{k,0,nn}]

Formula

Appears to be the complement of A083329 in A089633.

A065263 Infinite binary tree inspired permutation of N: 1 -> 3, 11ab..yz -> 11ab..yz1, 10ab..y0 -> 10ab..y, 10ab..y1 -> 11AB..Y0 (where 1AB..Y0 is the complement of 0ab..y1).

Original entry on oeis.org

3, 1, 7, 2, 6, 13, 15, 4, 14, 5, 12, 25, 27, 29, 31, 8, 30, 9, 28, 10, 26, 11, 24, 49, 51, 53, 55, 57, 59, 61, 63, 16, 62, 17, 60, 18, 58, 19, 56, 20, 54, 21, 52, 22, 50, 23, 48, 97, 99, 101, 103, 105, 107, 109, 111, 113, 115, 117, 119, 121, 123, 125, 127, 32, 126, 33, 124
Offset: 1

Views

Author

Antti Karttunen, Oct 28 2001

Keywords

Comments

When an infinite planar binary tree is mapped breadth-first-wise from left to right (1 is at top, 2 is its left and 3 its right child, 4 is 2's left child, etc.) then this permutation induces such rearrangement of its nodes, that on the right side every node replaces its right child, on the left side the left children replace their parents and the right children are reflected to the right side, to be the left children of their new parents.

Crossrefs

A057114, A065269, A065275, A065281, A065287. Inverse: A065264, conjugated with A059893: A065265 and the inverse of that: A065266.

Programs

  • Maple
    RightChildInverted := proc(n) local k; if(1 = n) then RETURN(3); fi; k := floor_log_2(n)-1; if(3 = floor(n/(2^k))) then RETURN((2*n)+1); fi; if(0 = (n mod 2)) then RETURN(n/2); fi; RETURN(2^(k+1) + ((2^(k+2))-1) - n); end;

A065269 Infinite binary tree inspired permutation of N: 1 -> 1, 11ab..yz -> 11ab..yz0, 10ab..y1 -> 10ab..y, 10ab..y0 -> 11AB..Y1 (where 1AB..Y1 is the complement of 0ab..y0).

Original entry on oeis.org

1, 3, 6, 7, 2, 12, 14, 15, 4, 13, 5, 24, 26, 28, 30, 31, 8, 29, 9, 27, 10, 25, 11, 48, 50, 52, 54, 56, 58, 60, 62, 63, 16, 61, 17, 59, 18, 57, 19, 55, 20, 53, 21, 51, 22, 49, 23, 96, 98, 100, 102, 104, 106, 108, 110, 112, 114, 116, 118, 120, 122, 124, 126, 127, 32, 125, 33
Offset: 1

Views

Author

Antti Karttunen, Oct 28 2001

Keywords

Comments

On the right side every node replaces its left child, on the left side the right children replace their parents and the left children are reflected to the right side (becoming right children). See comment at A065263.

Crossrefs

A057114, A065263, A065275, A065281, A065287. Inverse: A065270, conjugated with A059893: A065271 and the inverse of that: A065272.

Programs

  • Maple
    LeftChildInverted := proc(n) local k; if(1 = n) then RETURN(1); fi; k := floor_log_2(n)-1; if(3 = floor(n/(2^k))) then RETURN(2*n); fi; if(1 = (n mod 2)) then RETURN((n-1)/2); fi; RETURN(2^(k+1) + ((2^(k+2))-1) - n); end;
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