|
|
A057167
|
|
Term in Recamán's sequence A005132 where n appears for first time, or -1 if n never appears.
|
|
21
|
|
|
0, 1, 4, 2, 131, 129, 3, 5, 16, 14, 12, 10, 8, 6, 31, 29, 27, 25, 23, 99734, 7, 9, 11, 13, 15, 17, 64, 62, 60, 58, 56, 54, 52, 50, 48, 46, 44, 42, 40, 38, 111, 22, 20, 18, 28, 30, 32, 222, 220, 218, 216, 214, 212, 210, 208, 206, 204, 202, 200, 198, 196
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
0,3
|
|
LINKS
|
|
|
MAPLE
|
w := array(1..10000); for j from 1 to 100 do l := 0; for k from 1 to nops(a) do if a[k] = j then l := k; exit; fi; od: w[j] := l; od: s := [seq(w[j], j=1..100)]; # where a is an array formed from sequence A005132
|
|
MATHEMATICA
|
A005132 = {0}; Do[If[(r = Last[A005132] - n) <= 0 || MemberQ[ A005132, r], r = r + 2n]; AppendTo[ A005132, r], {n, 1, 10^5}]; a[n_] := If[p = Position[ A005132, n]; p == {}, 0, p[[1, 1]] - 1]; Table[a[n], {n, 1, 60}] (* Jean-François Alcover, Jul 18 2012 *)
|
|
PROG
|
(PARI) first(n) = my(a=vector(n), r=[0]); while(#Set(a)<n, my(i=#r, j=r[i]-i, k=j+(j<1 || setsearch(Set(r), j))*2*i); r=concat(r, [k]); if(k<n && !a[k+1], a[k+1]=i)); a \\ Iain Fox, Jul 11 2022
(Python)
from itertools import count, islice
def agen(): # generator of terms
an, A005132set, inv, y = 0, {0}, {0: 0}, 0
for n in count(1):
t = an - n
an = t if t >= 0 and t not in A005132set else an + n
A005132set.add(an)
inv[an] = n
while y in inv: yield inv[y]; y += 1
|
|
CROSSREFS
|
|
|
KEYWORD
|
|
|
AUTHOR
|
|
|
EXTENSIONS
|
a(0)=0 added and escape clause value changed to -1 by N. J. A. Sloane, May 01 2020
|
|
STATUS
|
approved
|
|
|
|