cp's OEIS Frontend

A286291 A bisection of A064736.

%I A286291 #34 Jan 17 2024 09:11:55
%S A286291 2,3,4,5,7,8,9,10,11,13,14,15,16,17,18,19,21,22,23,24,25,26,27,28,29,
%T A286291 30,31,32,33,34,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,
%U A286291 54,55,57,58,59,60,61,62,63,64,65,66,67,68,69,70,71,73,74,75,76,77,78,79,80,81,82,83,84,85
%N A286291 A bisection of A064736.
%C A286291 The terms of A064736 lie on two (curved) lines; this is one of them.
%C A286291 Sequence is: a(1) = 2, a(2) = 3. m is in the sequence if and only if there is no i such that a(i) * a(i+1) = m, where i are indices of terms in the sequence so far. By definition, this is the complement of A286090. - _David A. Corneth_, May 25 2017
%C A286291 Apparently the same as A121229 shifted by one place. - _R. J. Mathar_, May 25 2017
%H A286291 Ray Chandler, <a href="/A286291/b286291.txt">Table of n, a(n) for n = 1..10000</a>
%H A286291 Ray Chandler, <a href="/A286291/a286291_1M.gz">Table of n, a(n) for n = 1..1000000</a> (large gzipped file)
%e A286291 See comments: 4 is in the sequence, since the terms so far, 2 and 3, don't multiply to 4. Same for 5. Sequence so far is: 2, 3, 4, 5. 6 isn't in the sequence. 7 is. Carrying on we get 2, 3, 4, 5, 7, 8, 9, 10, 11. 12 isn't in the sequence. Further in the sequence, 30 is in the sequence though it's of the form k*(k+1) for k = 5. But 6 isn't in the sequence. And indeed, 5 and 7 are consecutive terms so 5*7 = 35 isn't in the sequence. - _David A. Corneth_, May 25 2017
%o A286291 (PARI) upto(n) = {my(l=List([2,3]), i = 1, p = 6, op = 3);
%o A286291 while(1, if(op>=n, return(l)); for(j=op + 1, p-1, listput(l, j)); i++; op = p; p = l[i]*l[i+1])}
%o A286291 is(n) = !is_A286290(n)
%o A286291 is_A286290(n) = if(n < 6, return(n==1)); if(issquare(n+1, &n), is(n), if(sqrtint(4*n+1)^2 == 4*n+1, s = sqrtint(4*n+1); !(is(s\2) || is(s\2+1)), return(0))) \\ _David A. Corneth_, May 25 2017
%Y A286291 Cf. A064736, A286290, A286292, A286293, A121229.
%K A286291 nonn
%O A286291 1,1
%A A286291 _N. J. A. Sloane_, May 23 2017