

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(n1)) >= 6.


2



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
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OFFSET

1,2


COMMENTS

A permutation of the natural numbers.


LINKS

Ivan Neretin and 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), 437446.
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


MAPLE

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(n1))<6 do od;
ina(k):= true; k
fi
end;
seq(a(n), n=1..60);


MATHEMATICA

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


PROG

(Python)
from sympy import gcd
l=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+=[k, ]
print l # Indranil Ghosh, Jun 27 2017


CROSSREFS

Cf. A064413, A064417, A064418, A064419, A262434 (inverse).
Sequence in context: A032989 A322570 A108320 * A032941 A273733 A218345
Adjacent sequences: A177955 A177956 A177957 * A177959 A177960 A177961


KEYWORD

nonn,easy,changed


AUTHOR

Jonathan Vos Post, Dec 16 2010


EXTENSIONS

Edited by Alois P. Heinz, Dec 16 2010


STATUS

approved



