A006877 In the '3x+1' problem, these values for the starting value set new records for number of steps to reach 1. (Formerly M0748)

1, 2, 3, 6, 7, 9, 18, 25, 27, 54, 73, 97, 129, 171, 231, 313, 327, 649, 703, 871, 1161, 2223, 2463, 2919, 3711, 6171, 10971, 13255, 17647, 23529, 26623, 34239, 35655, 52527, 77031, 106239, 142587, 156159, 216367, 230631, 410011, 511935, 626331, 837799

Offset

1,2

Comments

Both the 3x+1 steps and the halving steps are counted.

This sequence without a(2) = 2 specifies where records occur in A208981. - Omar E. Pol, Apr 14 2022

References

D. R. Hofstadter, Goedel, Escher, Bach: an Eternal Golden Braid, Random House, 1980, p. 400.

N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

Links

T. D. Noe, Table of n, a(n) for n = 1..130 (from Eric Roosendaal's data)

T. Ahmed and H. Snevily, Are there an infinite number of Collatz integers?, 2013.

Gaston H. Gonnet, Computations on the 3n+1 conjecture, Maple Technical Newsletter 6 (1991): 18-22.

Brian Hayes, Computer Recreations: On the ups and downs of hailstone numbers, Scientific American, 250 (No. 1, 1984), pp. 10-16.

J. C. Lagarias, The 3x+1 problem and its generalizations, Amer. Math. Monthly, 92 (1985), 3-23.

G. T. Leavens and M. Vermeulen, 3x+1 search programs, Computers and Mathematics with Applications, 24 (1992), 79-99. (Annotated scanned copy)

R. Munafo, Integer Sequences Related to 3x+1 Collatz Iteration

Eric Roosendaal, 3x+1 Delay Records

Robert G. Wilson v, Letter to N. J. A. Sloane with attachments, Jan. 1989

Robert G. Wilson v, Tables of A6877, A6884, A6885, Jan. 1989

Index entries for sequences from "Goedel, Escher, Bach"

Index entries for sequences related to 3x+1 (or Collatz) problem

David Barina, Convergence verification of the Collatz problem, The Journal of Supercomputing 77(3) (2021), 2681-2688.

David Barina, Computational Verification of the Collatz Problem, preprint on Research Square (2024).

Maple

A006877 := proc(n) local a, L; L := 0; a := n; while a <> 1 do if a mod 2 = 0 then a := a/2; else a := 3*a+1; fi; L := L+1; od: RETURN(L); end;

Mathematica

numberOfSteps[x0_] := Block[{x = x0, nos = 0}, While [x != 1 , If[Mod[x, 2] == 0 , x = x/2, x = 3*x + 1]; nos++]; nos]; a[1] = 1; a[n_] := a[n] = Block[{x = a[n-1] + 1}, record = numberOfSteps[x - 1]; While[ numberOfSteps[x] <= record, x++]; x]; A006877 = Table[ Print[a[n]]; a[n], {n, 1, 44}](* Jean-François Alcover, Feb 14 2012 *)
DeleteDuplicates[Table[{n, Length[NestWhileList[If[EvenQ[#], #/2, 3#+1]&, n, #>1&]]}, {n, 838000}], GreaterEqual[#1[[2]], #2[[2]]]&][[All, 1]] (* Harvey P. Dale, May 13 2022 *)

Prog

(PARI) A006577(n)=my(s); while(n>1, n=if(n%2, 3*n+1, n/2); s++); s
step(n, r)=my(t); forstep(k=bitor(n, 1), 2*n, 2, t=A006577(k); if(t>r, return([k, t]))); [2*n, r+1]
r=0; print1(n=1); for(i=1, 100, [n, r]=step(n, r); print1(", "n)) \\ Charles R Greathouse IV, Apr 01 2013
(Python)
c1 = lambda x: (3*x+1 if (x%2) else x>>1)
r = -1
for n in range(1, 10**5):
    a=0 ; n1=n
    while n>1: n=c1(n); a+=1;
    if a > r: print(n1, end = ', '); r=a
print('...') # Ya-Ping Lu and Robert Munafo, Mar 22 2024

Crossrefs

Cf. A006884, A006885, A006877, A006878, A033492.

Sequence in context: A018700 A018295 A033495 * A328832 A263881 A208892

Adjacent sequences: A006874 A006875 A006876 * A006878 A006879 A006880

Keyword

nonn,nice

Author

N. J. A. Sloane, Robert Munafo

Status

approved