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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A164287 Sequence resulting from an infinite series of reordering steps applied to the sequence of natural numbers A000027: At step n number n is moved from its position p to position p+k, where k is the actual number at position p+1.

Original entry on oeis.org

1, 3, 2, 4, 5, 8, 6, 7, 9, 12, 13, 10, 11, 16, 14, 17, 18, 15, 20, 24, 19, 25, 21, 22, 23, 31, 26, 34, 27, 33, 28, 37, 29, 38, 36, 30, 39, 32, 35, 46, 44, 47, 40, 48, 41, 42, 43, 49, 50, 53, 45, 58, 51, 59, 61, 52, 67, 54, 68, 55, 69, 56, 70, 57, 60, 73, 62, 63, 64, 65, 66, 80
Offset: 1

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Author

Eric Angelini and Alois P. Heinz, Aug 12 2009

Keywords

Comments

This sequence is a permutation of the natural numbers.

Crossrefs

Cf. A164286.

Programs

  • Maple
    mx:= 620: # increase mx to get more items
    l:= [i$i=1..2*mx]: pos:= proc(n) global l; local i; for i to nops(l) while l[i]<>n do od; `if`(i>nops(l), -1, i) end: for n from 1 to mx do p:= pos(n); k:= l[p+1]; l:= [l[1..p-1][], l[p+1..p+k][], l[p], l[p+k+1..nops(l)][]] od: p:= pos(mx+1): a:= n-> `if`(n
    				
  • Mathematica
    max = 200; r = Range[max]; For[n = 1, True, n++, p = Position[r, n]; If[p == {} || (q = p[[1, 1]] + r[[p[[1, 1]] + 1]] + 1) > max, Break[], c = r[[q]]; r = r /. {a___, n, b___, c, d___} :> {a, b, n, c, d}]]; A164287 = r[[1 ;; 72]] (* Jean-François Alcover, Jun 14 2012 *)

A164619 Integers of the form A164577(k)/3.

Original entry on oeis.org

4, 15, 54, 75, 132, 169, 320, 459, 735, 847, 1104, 1250, 1764, 2175, 2904, 3179, 3780, 4107, 5200, 6027, 7425, 7935, 9024, 9604, 11492, 12879, 15162, 15979, 17700, 18605, 21504, 23595, 26979, 28175, 30672, 31974, 36100, 39039, 43740, 45387, 48804
Offset: 1

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Author

Keywords

Comments

The sequence members are the third of the average of a set of smallest cubes, if integer.

Examples

			A third of the average of the first cube, A164577(1)/3=1/3, is not an integer and does not contribute to the sequence.
A third of the average of the first two cubes, A164577(2)/3=4, is an integer and defines a(1)=4 of the sequence.
		

Crossrefs

Programs

  • Mathematica
    s=0;lst={};Do[a=(s+=(n^3)/3)/n;If[Mod[a,1]==0,AppendTo[lst,a]],{n,2*5!}]; lst
    LinearRecurrence[{2,-1,-1,2,-1,2,-4,2,2,-4,2,-1,2,-1,-1,2,-1},{4,15,54,75,132,169,320,459,735,847,1104,1250,1764,2175,2904,3179,3780},50] (* Harvey P. Dale, Apr 06 2016 *)
  • PARI
    Vec(x*(x^14 +x^13 +16*x^12 +10*x^11 +47*x^10 -22*x^9 +61*x^8 +10*x^7 +88*x^6 +8*x^5 +43*x^4 -14*x^3 +28*x^2 +7*x +4) / ((x -1)^4*(x +1)^3*(x^2 -x +1)^3*(x^2 +x +1)^2) + O(x^100)) \\ Colin Barker, Oct 27 2014

Formula

a(n) = +2*a(n-1) -a(n-2) -a(n-3) +2*a(n-4) -a(n-5) +2*a(n-6) -4*a(n-7) +2*a(n-8) +2*a(n-9) -4*a(n-10) +2*a(n-11) -a(n-12) +2*a(n-13) -a(n-14) -a(n-15) +2*a(n-16) -a(n-17). - R. J. Mathar, Jan 25 2011
G.f.: x*(x^14 +x^13 +16*x^12 +10*x^11 +47*x^10 -22*x^9 +61*x^8 +10*x^7 +88*x^6 +8*x^5 +43*x^4 -14*x^3 +28*x^2 +7*x +4) / ((x -1)^4*(x +1)^3*(x^2 -x +1)^3*(x^2 +x +1)^2). - Colin Barker, Oct 27 2014

Extensions

Edited by R. J. Mathar, Aug 20 2009
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