A364863 Number of iterations of x -> x + min { k in A036301 | k > x } until an element of A036301 is reached, or -1 if this never happens, starting with n.

0, 21

Offset

0,2

Comments

The question whether the iteration always reaches an element of A036301 was raised on the SeqFan list in 2018, with "closest" instead of "next larger" (element of A036301). In that case one has 0 < n < 56 as a trivial counterexample. It is still open to our knowledge.

The first unknown term is currently a(2). Starting with x =2 we reach x = 336917039990529107004169 after 72 iterations.

Links

Table of n, a(n) for n=0..1.

Eric Angelini, Balanced/Unbalanced numbers (and iterations), personal blog "Cinquante signes" on blogspot,com, June 23, 2023

M. F. Hasler and N. J. A. Sloane, in reply to E. Angelini, Re: Balanced / Unbalanced numbers, Dec. 10, 2018

Formula

a(n) = 0 iff A071650(n) = 0, i.e., for all n in A036301.

Example

a(0) = 0 because n = 0 is an element of A036301 and therefore no iteration is required to reach such an element.
The smallest nonzero element of A036301 is 112. Therefore, all smaller positive numbers 0 < n < 112 go to n + 112 under the first iteration of
  f: x -> x + min { k in A036301 | k > x }.
Under iterations of f, 1 -> 113 -> 234 -> 548 -> 1109 -> 2229 -> 4460 -> 8931 -> 17865 -> 35872 -> 71875 -> 143891 -> 287898 -> 575804 -> 1151810 -> 2303826 -> 4607657 -> 9215347 -> 18430735 -> 36861480 -> 73723189 -> 147446477 which is the first element of A036301 to be reached, after a(1) = 21 iterations.

Prog

(PARI) a(n) = for(k=0, oo, A071650(n) || return(k); n+=next_A036301(n))

Crossrefs

Cf. A036301, A071650.

Sequence in context: A271976 A182370 A259331 * A209614 A167263 A324685

Adjacent sequences: A364860 A364861 A364862 * A364864 A364865 A364866

Keyword

nonn,base

Author

M. F. Hasler, Aug 11 2023

Status

approved