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.
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
Links
- 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
Programs
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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(n-1))<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 -
Python
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
Extensions
Edited by Alois P. Heinz, Dec 16 2010
Comments