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 A168007 Jumping divisor sequence (see Comments lines for definition). 3
 1, 2, 4, 3, 6, 5, 10, 9, 12, 11, 22, 21, 24, 23, 46, 45, 48, 47, 94, 93, 96, 95, 100, 99, 102, 101, 202, 201, 204, 203, 210, 209, 220, 219, 222, 221, 234, 233, 466, 465, 468, 467, 934, 933, 936, 935, 940, 939, 942, 941, 1882, 1881, 1884, 1883, 1890, 1889, 3778, 3777, 3780, 3779, 7558, 7557, 7560, 7559 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Consider the diagram with overlapping periodic curves that appears in the Links section (figure 2). The number of curves that contain the point [n,0] equals the number of divisors of n. The curve of diameter d represents the divisor d of n. Now consider only the lower part of the diagram (figure 3). Starting from point [1,0] we continue our journey walking along the semicircumference with smallest diameter not used previously (see the illustration of initial terms, figure 1). The sequence is formed by the values of n where the trajectory intercepts the x axis. - Omar E. Pol, Jan 14 2019 LINKS Jinyuan Wang, Table of n, a(n) for n = 1..1000 Omar E. Pol, Illustration of initial terms (Fig. 1) Omar E. Pol, Periodic curves and tau(n) (Fig. 2) FORMULA a(1) = 1; if a(n) is an even composite number then a(n+1) = a(n) - 1; otherwise a(n+1) = a(n) + A020639(a(n)). - Omar E. Pol, Jan 13 2019 PROG (PARI) lista(nn) = {my(v=vector(nn, i, if(i<4, 2^i/2))); for(n=4, nn, if(v[n-1]%2, v[n]=v[n-1] + factor(v[n-1])[1, 1], v[n]=v[n-1] - 1)); v; } \\ Jinyuan Wang, Mar 14 2020 CROSSREFS Cf. A000005, A002808, A020639, A004280, A168008, A168009. Sequence in context: A116533 A087559 A193298 * A328108 A091850 A332450 Adjacent sequences:  A168004 A168005 A168006 * A168008 A168009 A168010 KEYWORD nonn,easy AUTHOR Omar E. Pol, Nov 19 2009 EXTENSIONS More terms from Omar E. Pol, Jan 12 2019 STATUS approved

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Last modified April 14 07:59 EDT 2021. Contains 342946 sequences. (Running on oeis4.)