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.

Showing 1-3 of 3 results.

A073341 Number of steps to reach an integer starting with (2n+1)/4 and iterating the map x -> x*ceiling(x).

Original entry on oeis.org

3, 2, 3, 8, 1, 1, 3, 2, 2, 3, 2, 2, 1, 1, 7, 4, 4, 2, 4, 3, 1, 1, 2, 4, 2, 8, 4, 3, 1, 1, 6, 4, 3, 2, 5, 4, 1, 1, 5, 2, 2, 3, 2, 2, 1, 1, 4, 5, 6, 2, 3, 5, 1, 1, 2, 3, 2, 4, 3, 6, 1, 1, 7, 8, 3, 2, 4, 5, 1, 1, 3, 2, 2, 3, 2, 2, 1, 1, 7, 3, 4, 2, 7, 6, 1, 1, 2, 5, 2, 5, 5, 3, 1, 1, 3, 3, 3, 2, 10, 3, 1, 1, 4, 2, 2
Offset: 2

Views

Author

N. J. A. Sloane and J. C. Lagarias, Sep 04 2002

Keywords

Comments

We conjecture that an integer is always reached.
Is S(n) = Sum_{k=2..n} a(k) asymptotic to 3*n? S(n) = 3n for n = 69, 127, 166, 169, 189, 197, 327, 328, 360, 389, 404, 405, 419, 428, 497, 519, 520, 540, 541, 544, 547, 652, 668, 669, 676, 682, 683...
The sign of 3n-S(n) seems to change often: 3n-S(n) = 3, 4, 4, -1, 1, 3, 3, 4, 5, 5, 6, 7, 9, 11, 7, 6, 5, 6, 5, 5, 7, 9, 10, 9, 10, 5, 4, 4, 6, 8, 5, 4, 4, 5, 3, 2, 4, 6, 4, 5, 6, 6, 7, 8, 10, 12, 11, 9, 6, 7, 7, 5, 7, 9, 10, 10, 11, 10, 10, 7, 9, 11, 7, 2, 2, 3, 2, 0, 2, 4, 4, 5, 6, 6, 7, 8, 10, 12, 8, 8, 7, 8, 4, 1, 3, 5, 6, 4, 5, 3, 1, 1, 3, 5, 5, 5, 5, 6, -1, ... Is 3n-S(n) bounded? - Benoit Cloitre, Sep 05 2002

Links

Crossrefs

Cf. A073524, A074735, A085785, A085817, A085833.

Programs

  • Maple
    g := proc(x) local M,t1,t2,t3; M := 4^100; t1 := ceil(x) mod M; t2 := x*t1; t3 := numer(t2) mod M; t3/denom(t2); end;
a := []; for n from 2 to 150 do t1 := (2*n+1)/4; for i from 1 to 100 do t1 := g(t1); if type(t1,`integer`) then break; fi; od: a := [op(a),i]; od: a;
  • Mathematica
    a[n_] := Length @ NestWhileList[# Ceiling[#]&, (2n+1)/4, !IntegerQ[#]&] - 1;
Table[a[n], {n, 2, 100}] (* Jean-François Alcover, Jan 31 2023 *)
  • PARI
    a(n)=if(n<1,0,s=n/2+1/4; c=0; while(frac(s)>0,s=s*ceil(s); c++); c) \\ Benoit Cloitre, Sep 05 2002

A085785 Start at (2n+1)/4 and iterate the map x -> x*ceiling(x); sequence gives number of steps for denominator to drop to 1 or 2; or -1 if this never happens.

Original entry on oeis.org

1, 1, 3, 7, 1, 1, 2, 2, 1, 1, 2, 2, 1, 1, 6, 3, 1, 1, 4, 3, 1, 1, 2, 2, 1, 1, 2, 2, 1, 1, 3, 3, 1, 1, 5, 3, 1, 1, 2, 2, 1, 1, 2, 2, 1, 1, 3, 4, 1, 1, 3, 5, 1, 1, 2, 2, 1, 1, 2, 2, 1, 1, 6, 7, 1, 1, 3, 5, 1, 1, 2, 2, 1, 1, 2, 2, 1, 1, 5, 3, 1, 1, 5, 3, 1, 1, 2, 2, 1, 1, 2, 2, 1, 1, 3, 3, 1, 1, 8, 3, 1, 1, 2, 2, 1
Offset: 2

Views

Author

N. J. A. Sloane, Aug 16 2003

Keywords

Comments

We conjecture that the denominator always does drop.

Links

  • J. C. Lagarias and N. J. A. Sloane, Approximate squaring (pdf, ps), Experimental Math., 13 (2004), 113-128.

Crossrefs

A073341 gives number of steps until reach an integer. Cf. A085817, A085833.

A085817 Start at (2n+1)/4 and iterate the map x -> x*ceiling(x); sequence gives values of n for which the denominators in the orbit drop directly from 4 to 1, bypassing 2.

Original entry on oeis.org

4, 6, 7, 9, 12, 13, 14, 15, 20, 21, 22, 23, 24, 30, 31, 36, 38, 39, 41, 44, 45, 46, 47, 52, 53, 54, 55, 56, 62, 63, 69, 70, 71, 73, 76, 77, 78, 79, 81, 86, 87, 88, 94, 95, 96, 97, 101, 102, 103, 105, 108, 109, 110, 111, 112, 118, 119, 120, 126, 127, 129, 132, 133, 134, 135, 137
Offset: 1

Views

Author

N. J. A. Sloane, Aug 16 2003

Keywords

Comments

No formula is known for these numbers.

Links

  • J. C. Lagarias and N. J. A. Sloane, Approximate squaring (pdf, ps), Experimental Math., 13 (2004), 113-128.

Crossrefs

Complement of A085833.
A073341 gives number of steps until reach an integer. Cf. A085785.
Showing 1-3 of 3 results.

Started in 1964 by Neil J. A. Sloane | Maintained by The OEIS Foundation Inc.

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