A064419 -id:A064419 - cp's OEIS frontend

A064959 Inverse permutation to A064419.

1, 2, 3, 4, 5, 11, 23, 18, 14, 6, 33, 12, 40, 24, 7, 19, 62, 13, 68, 8, 25, 34, 87, 17, 9, 41, 15, 26, 104, 10, 111, 20, 35, 63, 22, 16, 133, 69, 42, 21, 144, 27, 162, 36, 30, 88, 172, 28, 47, 31, 64, 43, 197, 29, 32, 46, 70, 105, 215, 38, 237, 112, 48, 52, 39, 37, 248, 65

Offset: 1

N. J. A. Sloane, Oct 30 2001

Reinhard Zumkeller, Table of n, a(n) for n = 1..10000
J. C. Lagarias, E. M. Rains and N. J. A. Sloane, The EKG sequence, Exper. Math. 11 (2002), 437-446.
Index entries for sequences related to EKG sequence
Index entries for sequences that are permutations of the natural numbers

Cf. A064419, A064413.

import Data.List (elemIndex)
import Data.Maybe (fromJust)
a064959 n = a064959_list !! (n-1)
a064959_list = map ((+ 1) . fromJust . (`elemIndex` a064419_list)) [1..]
-- Reinhard Zumkeller, Sep 17 2001

More terms from Naohiro Nomoto, Oct 31 2001

A177958 a(n) = n for n <= 6; for n > 6, a(n) is the smallest number not already used such that gcd(a(n), a(n-1)) >= 6.

Original entry on oeis.org

1, 2, 3, 4, 5, 6, 12, 18, 9, 27, 36, 24, 8, 16, 32, 40, 10, 20, 30, 15, 45, 54, 42, 7, 14, 21, 28, 35, 49, 56, 48, 60, 50, 25, 75, 90, 63, 70, 77, 11, 22, 33, 44, 55, 66, 72, 64, 80, 88, 96, 78, 13, 26, 39, 52, 65, 91, 84, 98, 105

Offset: 1

Jonathan Vos Post, Dec 16 2010

A permutation of the natural numbers.

Alois P. Heinz, Table of n, a(n) for n = 1..10000 (first 2000 terms from Ivan Neretin)
J. C. Lagarias, E. M. Rains and N. J. A. Sloane, The EKG sequence, Exper. Math. 11 (2002), 437-446.
J. C. Lagarias, E. M. Rains and N. J. A. Sloane, The EKG sequence, arXiv:math/0204011 [math.NT], 2002.
Index entries for sequences related to EKG sequence
Index entries for sequences that are permutations of the natural numbers

Cf. A064413, A064417, A064418, A064419, A262434 (inverse).

ina:= proc(n) evalb(n<7) end:
a:= proc(n) option remember;
      local k;
      if n<7 then n
      else for k while ina(k) or igcd (k, a(n-1))<6 do od;
           ina(k):= true; k
      fi
    end;
seq(a(n), n=1..60);

t=Range[6]; Do[k=7; While[MemberQ[t, k] || GCD[t[[-1]], k] < 6, k++]; AppendTo[t, k], {n, 7, 100}]; t

from sympy import gcd
l=list(range(1, 7))
for n in range(6, 101):
    k=7
    while k in l or gcd(l[n - 1], k)<6: k+=1
    l.append(k)
print(l) # Indranil Ghosh, Jun 27 2017

Edited by Alois P. Heinz, Dec 16 2010

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A064959 Inverse permutation to A064419.

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A177958 a(n) = n for n <= 6; for n > 6, a(n) is the smallest number not already used such that gcd(a(n), a(n-1)) >= 6.

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