cp's OEIS Frontend

A112975 Lexicographically earliest permutation of the natural numbers such that each term has a common divisor with at least two earlier terms, a(n)=n for n<4.

%I A112975 #12 May 08 2015 10:35:33
%S A112975 1,2,3,6,4,8,9,10,12,14,15,5,16,18,20,21,7,22,24,25,26,27,28,30,32,33,
%T A112975 11,34,35,36,38,39,13,40,42,44,45,46,48,49,50,51,17,52,54,55,56,57,19,
%U A112975 58,60,62,63,64,65,66,68,69,23,70,72,74,75,76,77,78,80,81,82,84,85,86
%N A112975 Lexicographically earliest permutation of the natural numbers such that each term has a common divisor with at least two earlier terms, a(n)=n for n<4.
%C A112975 Inverse: A112978; A112977(n) = a(a(n));
%C A112975 For n>3: n is prime iff a(n) < a(n-1); a(A112976(n)) = A000040(n).
%C A112975 For n>8, a(n) can be described as follows: all composite numbers in natural order, with primes inserted so that every prime p immediately follows 3p. - _Ivan Neretin_, Apr 26 2015
%H A112975 Ivan Neretin, <a href="/A112975/b112975.txt">Table of n, a(n) for n = 1..1000</a>
%H A112975 <a href="/index/Per#IntegerPermutation">Index entries for sequences that are permutations of the natural numbers</a>
%Y A112975 Cf. A089088.
%K A112975 nonn
%O A112975 1,2
%A A112975 _Reinhard Zumkeller_, Oct 08 2005