A171862 - OEIS

A171862

Index of first occurrence of n in A181391, or 0 if n never appears.

1, 3, 5, 20, 17, 12, 10, 66, 47, 24, 148, 44, 173, 121, 30, 35, 138, 41, 63, 89, 56, 105, 324, 101, 215, 110, 257, 142, 320, 225, 471, 72, 59, 81, 183, 539, 134, 92, 263, 168, 129, 548, 52, 199, 179, 228, 98, 297, 621, 670, 357, 156, 116, 1486, 475

(list; graph; refs; listen; history; text; internal format)

OFFSET

0,2

LINKS

N. J. A. Sloane and Reinhard Zumkeller, Table of n, a(n) for n = 0..10000 (terms 1..1594 from N. J. A. Sloane)

MATHEMATICA

nmax = 100;

seq[m_] := seq[m] = Module[{b, last}, b[_] = 0; last[_] = -1; last[0] = 2; nxt = 1; Do[hist = last[nxt]; b[n] = nxt; last[nxt] = n; nxt = 0; If[hist > 0, nxt = n - hist], {n, 3, m}];

A171862 = Array[b, m];

a[n_] := FirstPosition[A171862, n];

Table[a[n], {n, 0, nmax}] /. Missing["NotFound"] -> 0 // Flatten

];

seq[m = nmax];

seq[m = 2 m];

While[Print["m = ", m]; seq[m] != seq[m/2], m = 2 m; ];

seq[m] (* Jean-François Alcover, Aug 02 2018, borrowing some Maple code from N. J. A. Sloane *)

PROG

(Haskell)

import Data.List (elemIndex)

import Data.Maybe (fromJust)