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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

T. D. Noe, Table of n, a(n) for n=0..1642 (taking a(1355) from A064227)

Nick Hobson, Python program for this sequence

C. L. Mallows, Plot (jpeg) of first 10000 terms of A005132

C. L. Mallows, Plot (postscript) of first 10000 terms of A005132

N. J. A. Sloane, My favorite integer sequences, in Sequences and their Applications (Proceedings of SETA '98).

N. J. A. Sloane, FORTRAN program for A005132, A057167, A064227, A064228

Index entries for sequences related to Recamán's sequence

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

print(list(islice(agen(), 61))) # Michael S. Branicky, Jul 12 2022

CROSSREFS

Cf. A005132, A057165, A057166.

Cf. also A187943, A187922.

Sequence in context: A201228 A010319 A266069 * A355646 A096683 A158903

Adjacent sequences:  A057164 A057165 A057166 * A057168 A057169 A057170

KEYWORD

nonn,easy,nice,look

AUTHOR

N. J. A. Sloane, Sep 14 2000

EXTENSIONS

I conjecture a(n) is never -1 - but see A064227, A064228.

a(0)=0 added and escape clause value changed to -1 by N. J. A. Sloane, May 01 2020

STATUS

approved

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Last modified September 27 13:46 EDT 2022. Contains 357062 sequences. (Running on oeis4.)