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 A286291 A bisection of A064736. 5
 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, 30, 31, 32, 33, 34, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 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 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS The terms of A064736 lie on two (curved) lines; this is one of them. 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 Apparently the same as A121229 shifted by one place. - R. J. Mathar, May 25 2017 LINKS Ray Chandler, Table of n, a(n) for n = 1..10000 Ray Chandler, Table of n, a(n) for n = 1..1000000 (large gzipped file) EXAMPLE 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 PROG upto(n) = {my(l=List([2, 3]), i = 1, p = 6, op = 3); 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])} is(n) = !is_A286290(n) 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 CROSSREFS Cf. A064736, A286290, A286292, A286293, A121229. Sequence in context: A303234 A175233 A121229 * A286926 A145198 A083210 Adjacent sequences:  A286288 A286289 A286290 * A286292 A286293 A286294 KEYWORD nonn AUTHOR N. J. A. Sloane, May 23 2017 STATUS approved

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Last modified July 12 23:28 EDT 2020. Contains 335669 sequences. (Running on oeis4.)