A008896 3x - 1 sequence starting at 66.

66, 33, 98, 49, 146, 73, 218, 109, 326, 163, 488, 244, 122, 61, 182, 91, 272, 136, 68, 34, 17, 50, 25, 74, 37, 110, 55, 164, 82, 41, 122, 61, 182, 91, 272, 136, 68, 34, 17, 50, 25, 74, 37, 110, 55, 164, 82, 41, 122

Offset

0,1

References

R. K. Guy, Unsolved Problems in Number Theory, E16.

Links

Table of n, a(n) for n=0..48.

Index entries for linear recurrences with constant coefficients, signature (0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,1).

Formula

a(0) = 66, a(n) = a(n - 1)/2 if a(n - 1) is even, otherwise 3a(n - 1) - 1.

Mathematica

NestList[If[EvenQ[#], #/2, 3# - 1] &, 66, 50] (* or *) PadRight[ {66, 33, 98, 49, 146, 73, 218, 109, 326, 163, 488, 244}, 120, {68, 34, 17, 50, 25, 74, 37, 110, 55, 164, 82, 41, 122, 61, 182, 91, 272, 136}] (* Harvey P. Dale, Sep 02 2018 *)

Prog

(Scala) def collatz(n: Int): Int = n % 2 match {
  case 0 => n / 2
  case _ => 3 * n + 1
}
def collatzSeq(n: Int): LazyList[Int] = LazyList.iterate(n)(collatz)
collatzSeq(-33).take(100).toList.map(_ * -1) // Alonso del Arte, Apr 25 2020

Crossrefs

Cf. A008880 (3x + 1 sequence starting at 33).

Sequence in context: A271711 A138843 A033386 * A071712 A080592 A059175

Adjacent sequences: A008893 A008894 A008895 * A008897 A008898 A008899

Keyword

nonn,easy

Author

N. J. A. Sloane.

Extensions

More specific name from Alonso del Arte, Apr 25 2020 (was "x -> x/2 if x even, x -> 3x - 1 if x odd").

Status

approved