This site is supported by donations to The OEIS Foundation.

 Please make a donation to keep the OEIS running. We are now in our 55th year. In the past year we added 12000 new sequences and reached 8000 citations (which often say "discovered thanks to the OEIS"). We need to raise money to hire someone to manage submissions, which would reduce the load on our editors and speed up editing. Other ways to donate

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 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. 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 (list; graph; refs; listen; history; text; internal format)
 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), 437-446. J. C. Lagarias, E. M. Rains and N. J. A. Sloane, The EKG sequence, arXiv:math/0204011 [math.NT], 2002. 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 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

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified December 12 09:36 EST 2019. Contains 329953 sequences. (Running on oeis4.)